drm/xe: Read VF GMD_ID with a specifically-allocated dummy GT

SRIOV VF initialization has a bit of a chicken and egg design problem.
Determining the IP version of the graphics and media IPs can't be done
via direct register reads as it is on PF or native and instead requires
querying the GuC.  However initialization of the GT, including its GuC,
needs to wait until after we know the IP versions so that the proper
initialization steps for the platform/IP are followed.

Currently the (somewhat hacky) solution is to manually fill out just
enough fields in tile 0's primary GT structure to make it look as if the
GT has been initialized so that the GuC can be partially initialized and
queried to obtain the GMD_ID values.  When the GT gets properly
initialized during the regular flows, the hacked-up values will get
overwritten as part of the general initialization flows.

Rather than using tile 0's primary GT structure to hold the hacked up
values for querying every GT on every tile, instead allocate a dedicated
dummy structure.  This will allow us to move the tile->primary_gt's
allocation to a more consistent place later in the initialization flow
in future patches (i.e., we shouldn't even allocate this GT structure if
the GT is disabled/unavailable).  It also helps ensure there can't be
any accidental leakage of initialization or state between the dummy
initialization for GMD_ID and the real driver initialization of the GT.

v2:
 - Initialize gt->tile for temporary GT.  (CI, Michal)
 - Use scope-based cleanup handler to free temp GT.  (Michal)
 - Propagate actual error code from xe_gt_sriov_vf_bootstrap() rather
   than just setting IP version to 0.0 now that read_gmdid() can return
   an error.  (Michal)
v3:
 - Explicitly initialize gt to NULL, just in case something else gets
   inserted before the kzalloc() in the future.  (Lucas)

Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20251013200944.2499947-32-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>

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