drm/i915: Move PCH refclock stuff into its own file

drm/i915: Move PCH refclock stuff into its own file

Move the PCH refclk stuff (including all the LPT/WPT
iCLKIP/CLKOUT_DP things) to its own file.

We also suck in the mPHY programming from intel_fdi.c
since we're the only caller.

Cc: Dave Airlie <airlied@redhat.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211015071625.593-2-ville.syrjala@linux.intel.com
Reviewed-by: Dave Airlie <airlied@redhat.com>