drm/i915/gt: use intel_uncore_rmw when appropriate

This patch replaces all occurences of the form
intel_uncore_write(reg, intel_uncore_read(reg) OP val)
with intel_uncore_rmw.

Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221019143818.244339-2-andrzej.hajda@intel.com