drm/vmwgfx: Add a new enum for SM5 graphics context capability

A new enum to represent new SM5 graphics context capability in vmwgfx.

v2: use new correct cap bits (merged several later commits into it).

Signed-off-by: Deepak Rawat <drawat.floss@gmail.com>
Signed-off-by: Thomas Hellström (VMware) <thomas_os@shipmail.org>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Signed-off-by: Roland Scheidegger <sroland@vmware.com>