clk: sunxi-ng: a64: Export PLL_PERIPH0 clock for the PRCM

The PRCM takes PLL_PERIPH0 as one of its parents for the AR100 clock.
As such we need to be able to describe this relationship in the device
tree.

Export the PLL_PERIPH0 clock so we can reference it in the PRCM node.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>