drm/vmwgfx: Add and connect atomic state object check/commit

This connects the main state object check and commit function.

v2
* Use drm_atomic_helper_commit() rather than a vmwgfx-specific one

Signed-off-by: Sinclair Yeh <syeh@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Acked-by: Daniel Vetter <daniel@ffwll.ch>