xf86drmMode: simplify drm_property_type_is

No need to have two branches depending on DRM_MODE_PROP_EXTENDED_TYPE.
We can just use drmModeGetPropertyType instead.

This does introduce a slight change: previously, drm_property_type_is()
could be called with non-type flags such as IMMUTABLE. However no user
seems to do this (checked KWin/Mutter/Sway/Weston/Xorg).

Signed-off-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>