drm/radeon/ni_dma: Move 'cayman_gpu_check_soft_reset()'s prototype to shared header

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

 drivers/gpu/drm/radeon/ni.c:1733:5: warning: no previous prototype for ‘cayman_gpu_check_soft_reset’ [-Wmissing-prototypes]
 1733 | u32 cayman_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/ni.h

@@ -32,5 +32,6 @@ void cayman_cp_int_cntl_setup(struct radeon_device *rdev,
 			      int ring, u32 cp_int_cntl);
 void cayman_vm_decode_fault(struct radeon_device *rdev,
 			    u32 status, u32 addr);
+u32 cayman_gpu_check_soft_reset(struct radeon_device *rdev);
 
 #endif				/* __NI_H__ */

drivers/gpu/drm/radeon/ni_dma.c

@@ -25,10 +25,9 @@
 #include "radeon.h"
 #include "radeon_asic.h"
 #include "radeon_trace.h"
+#include "ni.h"
 #include "nid.h"
 
-u32 cayman_gpu_check_soft_reset(struct radeon_device *rdev);
-
 /*
  * DMA
  * Starting with R600, the GPU has an asynchronous