drm/xe: Defer memirq init until needed

drm/xe: Defer memirq init until needed

memirqs require allocations into GGTT, which we cannot use until
after display is enabled.

Now that the initialisation of interrupts is postponed, move memirq
init too.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Ilia Levi <ilia.levi@intel.com>
Link: https://lore.kernel.org/r/20250619104858.418440-14-dev@lankhorst.se
Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>