ARM: dts: sun8i: a83t: cubietruck-plus: Enable micro-SD card and eMMC

Now that we support the MMC controllers on the A83T SoC, we can enable
them on some boards.

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