drm/xe/irq: Don't clobber display interrupts on multi-tile platforms

Although our only multi-tile platform today (PVC) doesn't support
display, it's possible that some future multi-tile platform will.
If/when this happens, display interrupts (both traditional display and
ASLE backlight interrupts raised as a Gunit interrupt) should be
delivered to the primary tile.  Save away tile0's master_ctl value so
that it can still be used for display interrupt handling after the GT
loop.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20230401002106.588656-9-matthew.d.roper@intel.com


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