drm/radeon: add RADEON_GEM_NO_CPU_ACCESS BO creation flag (v4)

Allows pinning of buffers in the non-CPU visible portion of
vram.

v2: incorporate Michel's comments.
v3: rebase on Michel's patch
v4: rebase on Michel's v2 patch

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>

include/uapi/drm/radeon_drm.h

@@ -803,6 +803,8 @@ struct drm_radeon_gem_info {
 #define RADEON_GEM_GTT_WC		(1 << 2)
 /* BO is expected to be accessed by the CPU */
 #define RADEON_GEM_CPU_ACCESS		(1 << 3)
+/* CPU access is not expected to work for this BO */
+#define RADEON_GEM_NO_CPU_ACCESS	(1 << 4)
 
 struct drm_radeon_gem_create {
 	uint64_t	size;