drm/xe/irq: Move ASLE backlight interrupt logic

Our only use of GUnit interrupts is to handle ASLE backlight operations
that are reported as GUnit GSE interrupts.  Move the enable/disable of
these interrupts to a more sensible place, in the same area where we
expect display interrupt code to be added by future patches.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20230601215244.678611-23-matthew.d.roper@intel.com


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