allwinner: h6: power: Switch to using the AXP driver

Chip ID checking and poweroff work just like they did before.
Regulators are now enabled just like on A64/H5.

This changes the signatures of the low-level register read/write
functions to match the interface expected by the common driver.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Change-Id: I14d63d171a094fa1375904928270fa3e21761646
4 files changed