drm/i915: Move DDI clock readout to encoder->get_config()

drm/i915: Move DDI clock readout to encoder->get_config()

Move the *_get_ddi_pll() stuff into the encodet->get_config() hook.
There it neatly sits next to the matching .{enable,disable}_clock()
functions.

In order to avoid excessive boilerplate I changed the behaviour
such that all platforms now do the readout via
crtc_state->port_dpll[].

ICL+ TC is still a bit special due to TBTPLL not having a functional
.get_freq(). Should probably change that by adopting the LCPLL
approach, but that would require a fairly substantial rework of the
DPLL ID handling. So leave it for later.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210224144214.24803-5-ville.syrjala@linux.intel.com
Reviewed-by: Mika Kahola <mika.kahola@intel.com>