This is the plumbing for supporting fb modifiers on planes. Modifiers
have already been introduced to some extent, but this series will extend
this to allow querying modifiers per plane. Based on this, the client to
enable optimal modifications for framebuffers.

This patch simply allows the DRM drivers to initialize their list of
supported modifiers upon initializing the plane.

v2: A minor addition from Daniel

v3:
* Updated commit message
* s/INVALID/DRM_FORMAT_MOD_INVALID (Liviu)
* Remove some excess newlines (Liviu)
* Update comment for > 64 modifiers (Liviu)

v4: Minor comment adjustments (Liviu)

v5: Some new platforms added due to rebase

v6: Add some missed plane inits (or maybe they're new - who knows at
this point) (Daniel)

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Daniel Stone <daniels@collabora.com> (v2)
Reviewed-by: Liviu Dudau <Liviu.Dudau@arm.com>
Signed-off-by: Daniel Stone <daniels@collabora.com>

Allwinner have a new "Display Engine 2.0" in their new SoCs, which comes
with mixers to do graphic processing and feed data to TCON, like the old
backends and frontends.

Add support for the mixer on Allwinner V3s SoC; it's the simplest one.

Currently a lot of functions are still missing -- more investigations
are needed to gain enough information for them.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>