drm/radeon/evergreen_dma: Move 'evergreen_gpu_check_soft_reset()'s prototype to shared header

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

drivers/gpu/drm/radeon/evergreen.c:3825:5: warning: no previous prototype for ‘evergreen_gpu_check_soft_reset’ [-Wmissing-prototypes]
3825 | u32 evergreen_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/evergreen.h

···
 void evergreen_gpu_pci_config_reset(struct radeon_device *rdev);
 u32 evergreen_get_number_of_dram_channels(struct radeon_device *rdev);
 void evergreen_print_gpu_status_regs(struct radeon_device *rdev);
+u32 evergreen_gpu_check_soft_reset(struct radeon_device *rdev);
 
 #endif				/* __RADEON_EVERGREEN_H__ */

drivers/gpu/drm/radeon/evergreen_dma.c

···
 
 #include "radeon.h"
 #include "radeon_asic.h"
+#include "evergreen.h"
 #include "evergreend.h"
-
-u32 evergreen_gpu_check_soft_reset(struct radeon_device *rdev);
 
 /**
  * evergreen_dma_fence_ring_emit - emit a fence on the DMA ring