sunxi: Use SUN6I_PRCM if used

SUN6I_PRCM is also used for SUN8I and SUN9I, so
select the same on respective MACH types.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>