[][dts: mt7986: Add SPIM prefix to NOR dts and remove unnecessary ones]

[Description]
Add SPIM prefix to NOR dts and remove unnecessary ones. To avoid
misunderstanding, add spim prefix to nor images, too.

[Release-log]
N/A

Change-Id: I61f8ce68c7cc9ac87ac5a00b660a6ae7abb0541f
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/5395822
7 files changed