drm/xe/guc: Add PF2GUC_UPDATE_VGT_POLICY to ABI

In upcoming patches the PF driver will add support to change GuC
policies and will need to use PF2GUC_UPDATE_VGT_POLICY messages.
Add necessary definitions to our GuC firmware ABI header.

Reviewed-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240410170338.1199-4-michal.wajdeczko@intel.com