drm/radeon/cik_sdma: Move 'amdgpu_cik_gpu_check_soft_reset()'s prototype to shared header

Fixes the following W=1 kernel build warning(s):

drivers/gpu/drm/radeon/cik.c:4845:5: warning: no previous prototype for ‘cik_gpu_check_soft_reset’ [-Wmissing-prototypes]
4845 | u32 cik_gpu_check_soft_reset(struct radeon_device *rdev)
| ^~~~~~~~~~~~~~~~~~~~~~~~

Cc: Alex Deucher <[e-mail]>
Cc: "Christian König" <[e-mail]>
Cc: David Airlie <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Lee Jones <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/radeon/cik.h

···
 void cik_exit_rlc_safe_mode(struct radeon_device *rdev);
 int ci_mc_load_microcode(struct radeon_device *rdev);
 void cik_update_cg(struct radeon_device *rdev, u32 block, bool enable);
+u32 cik_gpu_check_soft_reset(struct radeon_device *rdev);
 
 #endif                         /* __CIK_H__ */

drivers/gpu/drm/radeon/cik_sdma.c

···
 #include "radeon_ucode.h"
 #include "radeon_asic.h"
 #include "radeon_trace.h"
+#include "cik.h"
 #include "cikd.h"
 
 /* sdma */
 #define CIK_SDMA_UCODE_SIZE 1050
 #define CIK_SDMA_UCODE_VERSION 64
-
-u32 cik_gpu_check_soft_reset(struct radeon_device *rdev);
 
 /*
  * sDMA - System DMA