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 <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/cik.h

@@ -29,5 +29,6 @@ void cik_enter_rlc_safe_mode(struct radeon_device *rdev);
 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

@@ -27,14 +27,13 @@
 #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
  * Starting with CIK, the GPU has new asynchronous