drm/i915: add wrappers around cdclk vtable funcs.

This adds wrappers around all the vtable callers so they are in
one place.

Suggested by Jani.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/c3dd7aaad039e76acde9dda7211468907aa657c0.1632869550.git.jani.nikula@intel.com