To properly verify the driver->doorbell->GuC functionality, validation
needs to know how the driver has assigned the doorbell cache lines and
registers, so make them visible through debugfs.

v2: use kernel bitmap-printing format (%pb) rather than %x.
Signed-off-by: NDave Gordon <david.s.gordon@intel.com>
Reviewed-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>