drm/i915/dsi: add separate init timer mask definition for ICL DSI

Having a separate definition will be useful for splitting VLV and ICL
register files.

Cc: Matt Roper <[e-mail]>
Reviewed-by: Matt Roper <[e-mail]>
Signed-off-by: Jani Nikula <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/i915/display/icl_dsi.c

···
 	/* Program T-INIT master registers */
 	for_each_dsi_port(port, intel_dsi->ports) {
 		tmp = intel_de_read(dev_priv, ICL_DSI_T_INIT_MASTER(port));
-		tmp &= ~MASTER_INIT_TIMER_MASK;
+		tmp &= ~DSI_T_INIT_MASTER_MASK;
 		tmp |= intel_dsi->init_count;
 		intel_de_write(dev_priv, ICL_DSI_T_INIT_MASTER(port), tmp);
 	}

drivers/gpu/drm/i915/i915_reg.h

···
 #define ICL_DSI_T_INIT_MASTER(port)	_MMIO_PORT(port,	\
 						   _ICL_DSI_T_INIT_MASTER_0,\
 						   _ICL_DSI_T_INIT_MASTER_1)
+#define   DSI_T_INIT_MASTER_MASK	REG_GENMASK(15, 0)
 
 #define _DPHY_CLK_TIMING_PARAM_0	0x162180
 #define _DPHY_CLK_TIMING_PARAM_1	0x6c180