ARM: sun8i: a33: add CPU thermal throttling

This adds CPU thermal throttling for the Allwinner A33. It uses the
thermal sensor present in the SoC's GPADC.

Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>