drm/i915: Pass encoder to intel_ddi_enable_pipe_clock()

Since intel_ddi_enable_pipe_clock() was pushed down into the
encoder hooks we can pass on the encoder instead of having
to use intel_ddi_get_crtc_encoder().

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200417134720.16654-1-ville.syrjala@linux.intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Jani Nikula <jani.nikula@intel.com>