drm/amd: Fix set but not used warnings

There are many set but not used warnings under drivers/gpu/drm/amd when
compiling with the latest upstream mainline GCC:

drivers/gpu/drm/amd/amdgpu/amdgpu_gart.c:305:18: warning: variable ‘p’ set but not used [-Wunused-but-set-variable=]
drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.h:103:26: warning: variable ‘internal_reg_offset’ set but not used [-Wunused-but-set-variable=]
...
drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.h:164:26: warning: variable ‘internal_reg_offset’ set but not used [-Wunused-but-set-variable=]
...
drivers/gpu/drm/amd/amdgpu/../display/dc/dc_dmub_srv.c:445:13: warning: variable ‘pipe_idx’ set but not used [-Wunused-but-set-variable=]
drivers/gpu/drm/amd/amdgpu/../display/dc/dc_dmub_srv.c:875:21: warning: variable ‘pipe_idx’ set but not used [-Wunused-but-set-variable=]

Remove the variables actually not used or add __maybe_unused attribute for
the variables actually used to fix them, compile tested only.

Signed-off-by: Tiezhu Yang <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/amdgpu/amdgpu_gart.c

···
 			int pages)
 {
 	unsigned t;
-	unsigned p;
 	int i, j;
 	u64 page_base;
 	/* Starting from VEGA10, system bit must be 0 to mean invalid. */
···
 		return;
 
 	t = offset / AMDGPU_GPU_PAGE_SIZE;
-	p = t / AMDGPU_GPU_PAGES_IN_CPU_PAGE;
-	for (i = 0; i < pages; i++, p++) {
+	for (i = 0; i < pages; i++) {
 		page_base = adev->dummy_page_addr;
 		if (!adev->gart.ptr)
 			continue;

drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.h

···
 
 #define SOC15_DPG_MODE_OFFSET(ip, inst_idx, reg) 						\
 	({											\
-		uint32_t internal_reg_offset, addr;						\
+		/* To avoid a -Wunused-but-set-variable warning. */				\
+		uint32_t internal_reg_offset __maybe_unused, addr;				\
 		bool video_range, video1_range, aon_range, aon1_range;				\
 												\
 		addr = (adev->reg_offset[ip##_HWIP][inst_idx][reg##_BASE_IDX] + reg);		\
···
 
 #define SOC24_DPG_MODE_OFFSET(ip, inst_idx, reg)						\
 	({											\
-		uint32_t internal_reg_offset, addr;						\
+		/* To avoid a -Wunused-but-set-variable warning. */				\
+		uint32_t internal_reg_offset __maybe_unused, addr;				\
 		bool video_range, video1_range, aon_range, aon1_range;				\
 												\
 		addr = (adev->reg_offset[ip##_HWIP][inst_idx][reg##_BASE_IDX] + reg);		\

drivers/gpu/drm/amd/display/dc/dc_dmub_srv.c

···
 	int i = 0, k = 0;
 	int ramp_up_num_steps = 1; // TODO: Ramp is currently disabled. Reenable it.
 	uint8_t visual_confirm_enabled;
-	int pipe_idx = 0;
 	struct dc_stream_status *stream_status = NULL;
 
 	if (dc == NULL)
···
 	cmd.fw_assisted_mclk_switch.config_data.visual_confirm_enabled = visual_confirm_enabled;
 
 	if (should_manage_pstate) {
-		for (i = 0, pipe_idx = 0; i < dc->res_pool->pipe_count; i++) {
+		for (i = 0; i < dc->res_pool->pipe_count; i++) {
 			struct pipe_ctx *pipe = &context->res_ctx.pipe_ctx[i];
 
 			if (!pipe->stream)
···
 				cmd.fw_assisted_mclk_switch.config_data.vactive_stretch_margin_us = dc->debug.fpo_vactive_margin_us;
 				break;
 			}
-			pipe_idx++;
 		}
 	}
 
···
 		bool enable)
 {
 	uint8_t cmd_pipe_index = 0;
-	uint32_t i, pipe_idx;
+	uint32_t i;
 	uint8_t subvp_count = 0;
 	union dmub_rb_cmd cmd;
 	struct pipe_ctx *subvp_pipes[2];
···
 
 	if (enable) {
 		// For each pipe that is a "main" SUBVP pipe, fill in pipe data for DMUB SUBVP cmd
-		for (i = 0, pipe_idx = 0; i < dc->res_pool->pipe_count; i++) {
+		for (i = 0; i < dc->res_pool->pipe_count; i++) {
 			struct pipe_ctx *pipe = &context->res_ctx.pipe_ctx[i];
 			pipe_mall_type = dc_state_get_pipe_subvp_type(context, pipe);
 
···
 				populate_subvp_cmd_vblank_pipe_info(dc, context, &cmd, pipe, cmd_pipe_index++);
 
 			}
-			pipe_idx++;
 		}
 		if (subvp_count == 2) {
 			update_subvp_prefetch_end_to_mall_start(dc, context, &cmd, subvp_pipes);