drm/i915: Use _MMIO_PIPE2() where appropriate

Stop hand rolling _MMIO_TRANS2() and just use the real thing.
Note that this register isn't even used atm, hence why this
builds despite the _PIPE2() macro not actually existing.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220623130900.26078-8-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>