clk: sunxi: add gating support to PLL1

This commit adds gating support to PLL1 on the clock driver. This makes
the PLL1 implementation fully compatible with PLL4 as well.

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