arm: dts: split mtk-reset.h into per-chip header

This follows the linux header rules to avoid conflict bitfields.

Tested-by: Frank Wunderlich <frank-w@public-files.de>
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Frank Wunderlich <frank-w@public-files.de>