[][Add factory label in mt7986 dts files]

[Description]
Add factory label in mt7986 dts files to make wifi driver able
to parse Factory partition with standard of_get_property() API.

[Release-log]
N/A

Change-Id: Ib5780bda3e25bfd645e930a1d5b45ffbca48ea22
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/4615428
5 files changed