drm: byteorder: add DRM_FORMAT_HOST_*

Add fourcc variants in host byte order.  With these at hand we don't
need #ifdefs in drivers which support framebuffers in cpu endianess.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20180905060445.15008-3-kraxel@redhat.com