drm/i915: Reduce bigjoiner special casing

Try to make bigjoiner pipes less special.

The main things here are that each pipe now does full
clock computation/readout with its own shared_dpll reference.
Also every pipe's cpu_transcoder always points correctly
at the master transcoder.

Due to the above changes state readout is now complete
and all the related hacks can go away. The actual modeset
sequence code is still a mess, but I think in order to clean
that up properly we're probably going to have to redesign
the modeset logic to treat transcoders vs. pipes separately.
That is going to require significant amounts of work.

Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211022103304.24164-9-ville.syrjala@linux.intel.com