drm/fourcc: Fix undefined left shift in DRM_FORMAT_BIG_ENDIAN macros

1<<31 is undefined because it's a signed int and C is terrible.

Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
Signed-off-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191018175041.613780-1-ajax@redhat.com