i2c: sun6i_p2wi: Add support for DM clocks and resets

Currently, clock/reset setup for this device is handled by a
platform-specific function and is intermixed with non-DM pinctrl
setup. Use the devicetree to get clocks/resets, which disentagles
it from the pinctrl setup in preparation for moving to DM_PINCTRL.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>