clk: sunxi-ng: h616: Add PLL derived 32KHz clock

The RTC section of the H616 manual mentions in a half-sentence the
existence of a clock "32K divided by PLL_PERI(2X)". This is used as
one of the possible inputs for the mux that selects the clock for the
32 KHz fanout pad. On the H616 this is routed to pin PG10, and some
boards use that clock output to compensate for a missing 32KHz crystal.
On the OrangePi Zero2 this is for instance connected to the LPO pin of
the WiFi/BT chip.
The new RTC clock binding requires this clock to be named as one input
clock, so we need to expose this to the DT. In contrast to the D1 SoC
there does not seem to be a gate for this clock, so just use a fixed
divider clock, using a newly assigned clock number.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://lore.kernel.org/r/20220428230933.15262-3-andre.przywara@arm.com