Revert "ARM: mediatek: add MT7623a smp bringup code"

This reverts commit 3b99ab7d.

The compatible "mediatek,mt7623a" is useless, so remove it.

Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>