clk: mediatek: add driver for MT8516

Add clock driver for MediaTek MT8516 SoC.

Signed-off-by: Fabien Parent <fparent@baylibre.com>
Acked-by: Ryder Lee <ryder.lee@mediatek.com>
[trini: Redo whitespace]
Signed-off-by: Tom Rini <trini@konsulko.com>