drm: drm_fourcc: Add uncompressed AFBC modifier

AFBC has a mode that guarantees use of AFBC with an uncompressed
payloads, we add a new modifier to support this mode.

V2: updated modifier comment
Signed-off-by: Ben Davis <ben.davis@arm.com>
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200430083220.17347-1-ben.davis@arm.com

include/uapi/drm/drm_fourcc.h

@@ -808,6 +808,18 @@ extern "C" {
  */
 #define AFBC_FORMAT_MOD_BCH     (1ULL << 11)
 
+/* AFBC uncompressed storage mode
+ *
+ * Indicates that the buffer is using AFBC uncompressed storage mode.
+ * In this mode all superblock payloads in the buffer use the uncompressed
+ * storage mode, which is usually only used for data which cannot be compressed.
+ * The buffer layout is the same as for AFBC buffers without USM set, this only
+ * affects the storage mode of the individual superblocks. Note that even a
+ * buffer without USM set may use uncompressed storage mode for some or all
+ * superblocks, USM just guarantees it for all.
+ */
+#define AFBC_FORMAT_MOD_USM	(1ULL << 12)
+
 /*
  * Arm 16x16 Block U-Interleaved modifier
  *