clk: sunxi-ng: Support separately grouped PLL lock status register

On the Allwinner A80 SoC, the PLL lock status indicators are grouped
together in a separate register, as opposed to being scattered in each
PLL's configuration register.

Add a flag to support this.

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