drm/radeon/radeon_drv: Move 'radeon_mmap()'s prototype to shared header

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

 drivers/gpu/drm/radeon/radeon_ttm.c:931:5: warning: no previous prototype for ‘radeon_mmap’ [-Wmissing-prototypes]
 931 | int radeon_mmap(struct file *filp, struct vm_area_struct *vma)
 | ^~~~~~~~~~~

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: Gareth Hughes <gareth@valinux.com>
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/radeon_drv.c

@@ -51,6 +51,7 @@
 #include <drm/radeon_drm.h>
 
 #include "radeon_drv.h"
+#include "radeon_ttm.h"
 #include "radeon_device.h"
 
 /*
@@ -126,7 +127,6 @@ extern int radeon_get_crtc_scanoutpos(struct drm_device *dev, unsigned int crtc,
 extern bool radeon_is_px(struct drm_device *dev);
 extern const struct drm_ioctl_desc radeon_ioctls_kms[];
 extern int radeon_max_kms_ioctl;
-int radeon_mmap(struct file *filp, struct vm_area_struct *vma);
 int radeon_mode_dumb_mmap(struct drm_file *filp,
 			  struct drm_device *dev,
 			  uint32_t handle, uint64_t *offset_p);

drivers/gpu/drm/radeon/radeon_ttm.h

@@ -32,5 +32,6 @@ struct radeon_device;
 
 int radeon_ttm_init(struct radeon_device *rdev);
 void radeon_ttm_fini(struct radeon_device *rdev);
+int radeon_mmap(struct file *filp, struct vm_area_struct *vma);
 
 #endif				/* __RADEON_TTM_H__ */