drm/xe/mocs: Initialize MOCS index early

MOCS uc_index is used even before it is initialized in the following
callstack
    guc_prepare_xfer()
    __xe_guc_upload()
    xe_guc_min_load_for_hwconfig()
    xe_uc_init_hwconfig()
    xe_gt_init_hwconfig()

Do MOCS index initialization earlier in the device probe.

Signed-off-by: Balasubramani Vivekanandan <balasubramani.vivekanandan@intel.com>
Reviewed-by: Ravi Kumar Vodapalli <ravi.kumar.vodapalli@intel.com>
Link: https://lore.kernel.org/r/20250520142445.2792824-1-balasubramani.vivekanandan@intel.com


Signed-off-by: Matt Roper <matthew.d.roper@intel.com>