mfd: sun6i-prcm: Add support for Allwinner A23 PRCM

The Allwinner A23 SoC has a PRCM unit like the previous A31 SoC.
The differences are the AR100 clock can no longer be modified,
the APB0 clock has different divisors, and some clock gates are
gone.

This patch adds a compatible with a modified subdevice list for
the A23.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>