drm/i915/reg: fix g4x pipe data/link m/n register style

Adhere to the style described at the top of i915_reg.h.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/f55960ce8cdcf654e5de19274c7b67b3d3497550.1725974820.git.jani.nikula@intel.com


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