The GFX doorbell solution provides a mechanism for submission of
workload to the graphics hardware by a ring3 application without
the penalty of ring transition for each workload submission.

This feature is not currently used by the Linux drivers, but in
SR-IOV mode the doorbells are treated as shared resource and the
PF driver must be able to provision exclusive range of doorbells
IDs across all enabled VFs.

Introduce simple GuC doorbell ID manager that will be used by the
PF driver for VFs provisioning and can later be used by submission
code once we are ready to switch from H2G based notifications to
doorbells mechanism.

Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Piotr Piórkowski <piotr.piorkowski@intel.com>
Reviewed-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Link: https://lore.kernel.org/r/20231218190629.502-4-michal.wajdeczko@intel.comSigned-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>