arm: dts: mt7623: add nand nodes to the mt7623.dtsi file

Add NAND/EEC nodes to the mt7623.dtsi file.

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