drm/vmwgfx: check master authentication in surface_ref ioctls

With later commit we'll rework DRM authentication handling. Namely
DRM_AUTH will not be a requirement for DRM_RENDER_ALLOW ioctls.

Since vmwgfx does isolation for primary clients in different master
realms, the DRM_AUTH can be dropped.

The only place where authentication matters, is surface_reference ioctls
whenever a legacy (non-prime) handle is used. For those ioctls we call
vmw_surface_handle_reference(), where we explicitly check if the client
is both a) master and b) unauthenticated - bailing out as result.

Otherwise the usual isolation path kicks in and we're all good.

v2: Reword commit message, since the isolation work has landed.

Cc: VMware Graphics <linux-graphics-maintainer@vmware.com>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>