drm/vmwgfx: Add and connect plane helper functions

Refactor previous FB and cursor plane update code into their
atomic counterparts: check, update, prepare, cleanup, and disable.

These helpers won't be called until we flip on the atomic support
flag or set drm_crtc_funcs->set_config to using the atomic
helper.

v2:
* Removed unnecessary pinning of cursor surface
* Added a few function headers

v3:
* Set clip region equal to the destination region
* Fixed surface pinning policy
* Enable SVGA mode in vmw_sou_primary_plane_prepare_fb

Signed-off-by: Sinclair Yeh <syeh@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>