ARM: sun7i: fix PLL4 clock and add PLL8

Allwinner reworked the PLL4 clock in sun7i; so we need to change the
compatible. Additionally, PLL8 is compatible with this new PLL4
implementation, so let's add a node for it as well.

Signed-off-by: Emilio López <emilio@elopez.com.ar>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>