Enable CPU opp tables for Tanix TX6.

Also add the fixed regulator that provided vdd-cpu-gpu required for
CPU opp tables.

This voltage has been found using a voltmeter and could be wrong.
Tested-by: Jernej Škrabec <jernej.skrabec@gmail.com>
Signed-off-by: Clément Péron <peron.clem@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>