drm: no need to hold global mutex for static data

drm_getcap and drm_version ioctls only reads static data,
there is no need to protect them with drm_global_mutex,
so make them DRM_UNLOCKED

Signed-off-by: Ilija Hadzic <ihadzic@research.bell-labs.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>