drm/vc4: Advertise supported modifiers for planes

The IN_FORMATS blob allows the kernel to advertise to userspace which
format/modifier combinations are supported, per plane. Use this to
advertise that we support both T_TILED and linear.

v2:
  - Only advertise T_TILED for RGB (Eric)
  - Actually turn on allow_fb_modifiers (Eric)

Signed-off-by: Daniel Stone <daniels@collabora.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/170828/