drm: Reject unknown legacy bpp and depth for drm_mode_addfb ioctl

Since this is handling user provided bpp and depth, we need to sanity
check and propagate the EINVAL back rather than assume what the insane
client intended and fill the logs with DRM_ERROR.

v2: Check both bpp and depth match the builtin pixel format, and
introduce a canonical DRM_FORMAT_INVALID to reserve 0 against any future
fourcc.

v3: Mark up DRM_FORMAT_C8 as being {bpp:8, depth:8}

Testcase: igt/kms_addfb_basic/legacy-format
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180905153116.28924-1-chris@chris-wilson.co.uk

include/uapi/drm/drm_fourcc.h

@@ -71,6 +71,9 @@ extern "C" {
 
 #define DRM_FORMAT_BIG_ENDIAN (1<<31) /* format is big endian instead of little endian */
 
+/* Reserve 0 for the invalid format specifier */
+#define DRM_FORMAT_INVALID	0
+
 /* color index */
 #define DRM_FORMAT_C8		fourcc_code('C', '8', ' ', ' ') /* [7:0] C */