drm/i915/dpio: s/ddi/dpio/ for bxt/glk PHY stuff

Since all of this lives in intel_dpio_phy.c let's rename the
bxt/glk functions to have bxt_dpio_phy_ namespace.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240412175818.29217-7-ville.syrjala@linux.intel.com


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