drm/i915/psr: Restore PSR interrupt handler for HSW

Add the PSR interrupt handling code back for HSW. Looks like
the removal was never completed anyway since the irq setup
code was lest untouched.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230609141404.12729-8-ville.syrjala@linux.intel.com


Reviewed-by: Jouni Högander <jouni.hogander@intel.com>