drm/xe: Reorder GGTT init to earlier point in probe

GuC will need to be loaded earlier during probe. Having functional GGTT
is one of the prerequisites.
Also rename xe_ggtt_init_noalloc to xe_ggtt_init_early to match the new
call site.

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>