dt-bindings: clock: sunxi-ccu: Add pll-periph to PRCM's needed clocks

The AR100 clock in the PRCM has parents, one of which is pll-periph from
the main CCU.

Add it to the list of required clocks for the PRCM CCU.

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