drm/fourcc: Add macros to determine the modifier vendor

When working with framebuffer modifiers, it can be useful to extract the
vendor identifier or check a modifier against a given vendor identifier.
Add one macro that extracts the vendor identifier and a helper to check
a modifier against a given vendor identifier.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Daniel Stone <daniels@collabora.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210610111236.3814211-1-thierry.reding@gmail.com