ramips: convert HiWiFi devices MAC address to NVMEM format

ramips: convert HiWiFi devices MAC address to NVMEM format

For all HiWiFi series devices, the base MAC address is stored on
"bdinfo" partition, offset 0x18a, ASCII text format. The recently
introduced "mac-base" nvmem layout can handle the ASCII text now,
so it's time to move MAC address configurations to dts. There is
no valid MAC info in the "factory" partition, hence they will be
replaced with the correct ones.

Tested on HiWiFi HC5661A and HC5861.

Signed-off-by: Shiji Yang <yangshiji66@outlook.com>
Link: https://github.com/openwrt/openwrt/pull/18251
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>