drm/ttm: prevent moving of pinned BOs

We have checks for this in the individual drivers move callback, but
it's probably better to generally forbid that on a higher level.

Also stops exporting ttm_resource_compat() since that's not necessary
any more after removing the extra checks in vmwgfx.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230130120636.63765-6-matthew.auld@intel.com