drm/vmwgfx: Command parser fixes for DX

Implement support for a couple of missing commands and fix a command parser
error path. Also fix uninitialized devcaps and surface size computation.

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