ARM: configs: sunxi: Enable the PS/2 controller

The A20 has a PS/2 controller and we have a driver for it, so let's enable
it in our defconfig.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Link: https://lore.kernel.org/r/20200706132323.147562-1-maxime@cerno.tech