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