drm/xe/gsc: Implement WA 14018094691

The WA states that we need to keep the primary GT powered up during GSC
load to allow the GSC FW to access its registers. We also need to make
sure that one of the registers is locked before starting the load.

v2: fix location of register def (Matt)

Bspec: 55928
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240326224456.518548-1-daniele.ceraolospurio@intel.com