drm/xe: Use gsc_proxy_init_done to check proxy status

Expose gsc_proxy_init_done so that we can check if gsc proxy has
been initialized or not.

--v2
-Check if GSC FW is enabled before taking forcewake ref [Daniele]

--v3
-Directly call proxy check function inside if condition

Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240306024247.1857881-5-suraj.kandpal@intel.com