drm/i915: Use intel_ddi_clk_select() for FDI

drm/i915: Use intel_ddi_clk_select() for FDI

We want to put all DDI clock routing code into one place.
Unify the FDI enable sequence to use the standard function
instead of hand rolling its own. The disable sequence already
uses the normal thing.

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210205214634.19341-2-ville.syrjala@linux.intel.com
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>