drm/xe/uc: Store firmware binary in system-memory backed BO

The firmware loading for GuC is about to be moved, and will happen much
earlier in the probe process, when local-memory is not yet available.
While this has the potential to make the firmware loading process
slower, this is only happening during probe and full device reset.
Since both are not hot-paths - store all UC-like firmware in system
memory.

Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>