drm/i915/dpio: Give VLV DPIO group register a clearer name

Include _GRP in VLV DPIO PHY group access register define
names. Makes it more obvious where the accesses will land.
Also matches the naming used by BXT already.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240422083457.23815-11-ville.syrjala@linux.intel.com


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