drm: Create a format/modifier blob

Updated blob layout (Rob, Daniel, Kristian, xerpi)

v2:
* Removed __packed, and alignment (.+)
* Fix indent in drm_format_modifier fields (Liviu)
* Remove duplicated modifier > 64 check (Liviu)
* Change comment about modifier (Liviu)
* Remove arguments to blob creation, use plane instead (Liviu)
* Fix data types (Ben)
* Make the blob part of uapi (Daniel)

v3:
Remove unused ret field.
Change i, and j to unsigned int (Emil)

v4:
Use plane->modifier_count instead of recounting (Daniel)

v5:
Rename modifiers to modifiers_property (Ville)
Use sizeof(__u32) instead to reflect UAPI nature (Ville)
Make BUILD_BUG_ON for blob header size

Cc: Rob Clark <robdclark@gmail.com>
Cc: Kristian H. Kristensen <hoegsberg@gmail.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Daniel Stone <daniels@collabora.com> (v2)
Reviewed-by: Liviu Dudau <liviu@dudau.co.uk> (v2)
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com> (v3)
Signed-off-by: Daniel Stone <daniels@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170724034641.13369-2-ben@bwidawsk.net
diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
index d986225..74f6ff5 100644
--- a/drivers/gpu/drm/drm_mode_config.c
+++ b/drivers/gpu/drm/drm_mode_config.c
@@ -337,6 +337,13 @@
 		return -ENOMEM;
 	dev->mode_config.gamma_lut_size_property = prop;
 
+	prop = drm_property_create(dev,
+				   DRM_MODE_PROP_IMMUTABLE | DRM_MODE_PROP_BLOB,
+				   "IN_FORMATS", 0);
+	if (!prop)
+		return -ENOMEM;
+	dev->mode_config.modifiers_property = prop;
+
 	return 0;
 }