arm64: dts: allwinner: a64: add CPU clock to CPU0-3 nodes

Add CPU clock to the CPU nodes since it is a prerequisite for enabling
DVFS.

Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
[wens@csie.org: Replace CLK_CPUX macro with raw number]
Signed-off-by: Chen-Yu Tsai <wens@csie.org>