drm/xe/pf: Make sure PF is ready to configure VFs

drm/xe/pf: Make sure PF is ready to configure VFs

The PF driver might be resumed just to configure VFs, but since
it is doing some asynchronous GuC reconfigurations after fresh
reset, we should wait until all pending works are completed.

This is especially important in case of LMEM provisioning, since
we also need to update the LMTT and send invalidation requests
to all GuCs, which are expected to be already in the VGT mode.

Fixes: 68ae022278a1 ("drm/xe/pf: Force GuC virtualization mode")
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Cc: Jonathan Cavitt <jonathan.cavitt@intel.com>
Link: https://lore.kernel.org/r/20250801142822.180530-3-michal.wajdeczko@intel.com