ARM: sunxi: add PLL4 support

This commit adds the PLL4 definition to the sun4i, sun5i and sun7i
device trees. PLL4 is compatible with PLL1.

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