clk: sunxi-ng: sun6i-rtc: Add support for H6

H6 supports IOSC calibration and an ext-osc32k input. Unlike newer SoCs,
it has a single parent for its fanout clock.

Add support for H6 in the CCU driver, replacing the support in the
existing early OF clock provider.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220203021736.13434-7-samuel@sholland.org