clk: berlin: add driver for BG2x audio/video PLL

clk: berlin: add driver for BG2x audio/video PLL

This is a driver for the dual-VCO PLL with 8 channels each found on
Marvell Berlin2 SoCs. While both VCOs share the same register set,
sometimes registers shifts for one of the VCOs is a bit off. Nothing
serious that should require a separate driver, so deal with both VCOs
in a single driver instead.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>