drm/amdgpu: add AMDGPU_GEM_CREATE_DISCARDABLE

Add a AMDGPU_GEM_CREATE_DISCARDABLE flag to note that the content of a BO
doesn't needs to be preserved during eviction.

KFD was already using a similar functionality for SVM BOs so replace the
internal flag with the new UAPI.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

include/uapi/drm/amdgpu_drm.h

@@ -140,6 +140,10 @@ extern "C" {
  * not require GTT memory accounting
  */
 #define AMDGPU_GEM_CREATE_PREEMPTIBLE		(1 << 11)
+/* Flag that BO can be discarded under memory pressure without keeping the
+ * content.
+ */
+#define AMDGPU_GEM_CREATE_DISCARDABLE		(1 << 12)
 
 struct drm_amdgpu_gem_create_in  {
 	/** the requested memory size */