drm/i915: Nuke ilk_get_fdi_m_n_config()

Get rid of the entirely pointless ilk_get_fdi_m_n_config() wrapper
and just call the CPU transcoder function directly.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220128103757.22461-4-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>