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