clk: sunxi: Add additional RTC compatible strings

Compatible strings for some new RTC hardware variants were added to
the binding. Add them to the driver in preparation for supporting
those new SoCs.

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>