drm/i915: Clean up PIPECONF bit defines

Use REG_BIT() & co. for PIPECONF bits, and adjust the
naming of various bits to be more consistent.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211112193813.8224-5-ville.syrjala@linux.intel.com


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