headers: sync drm_fourcc.h with airlied/drm-next

This adds a bunch of modifiers stuff, as well as a few new formats.
Includes the following changes:
ebbb0e5cfd2ceb1150b1 drm: add extern C guard for the UAPI headers
b9fb2a21ac8058965a6b drm_fourcc: Document linear modifier
af913418261d6d3e7a29 drm_fourcc: Fix DRM_FORMAT_MOD_LINEAR #define
fd056f05b9fcba35b77e drm: add fourcc codes for 16bit R and RG
73f1a5858bf82f3bf232 drm/fourcc: add vivante tiled layout format modifiers
ba2b5277dc52cc96944d drm: add RGB formats with separate alpha plane
5e91144dd702d068b22a drm/tegra: Add tiling FB modifiers

Generated using `make headers_install` from airlied/drm-next
at commit 2a1720376adda5ecf8e636fbfb05339c7dad1c55

Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>