drm/i915/display: remove small micro-optimizations in irq handling

drm/i915/display: remove small micro-optimizations in irq handling

The raw register reads/writes are there as micro-optimizations to avoid
multiple pointer indirections on uncore->regs. Presumably this is useful
when there are plenty of register reads/writes in the same
function. However, the display irq handling only has a few raw
reads/writes. Remove them for simplification.

Reviewed-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Acked-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240408125445.3227678-1-jani.nikula@intel.com