drm/ttm: Define a single DRM_FILE_PAGE_OFFSET constant

Most TTM drivers define the constant DRM_FILE_PAGE_OFFSET of the same
value. The only exception is vboxvideo, which is being converted to the
new offset by this patch. Unifying the constants in a single place
simplifies the driver code.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Christian König <christian.koenig@amd.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/mgag200/mgag200_drv.h

@@ -269,7 +269,6 @@ mgag200_dumb_mmap_offset(struct drm_file *file,
 struct mga_i2c_chan *mgag200_i2c_create(struct drm_device *dev);
 void mgag200_i2c_destroy(struct mga_i2c_chan *i2c);
 
-#define DRM_FILE_PAGE_OFFSET (0x100000000ULL >> PAGE_SHIFT)
 void mgag200_ttm_placement(struct mgag200_bo *bo, int domain);
 
 static inline int mgag200_bo_reserve(struct mgag200_bo *bo, bool no_wait)