arm: dts: mt7623: Add SD-card and EMMC to bananapi-r2

The bananapi-r2 board has an SD-card controller and built-in
EMMC storage so enables those devices in the devicetree.

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>