clk: sunxi: Add driver for A80 MMC config clocks/resets

On the A80 SoC, the 4 mmc controllers each have a separate register
controlling their register access clocks and reset controls. These
registers in turn share a ahb clock gate and reset control.

This patch adds a platform device driver for these controls. It
requires both clocks and reset controls to be available, so using
CLK_OF_DECLARE might not be the best way.

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