drm/xe/uc: Move GuC submission init to post hwconfig step

We shouldn't need anything from the GuC submission code until we
finish GuC initialization in post hwconfig step.

While around add diagnostic message if we fail uC init.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240510203810.1952-3-michal.wajdeczko@intel.com