ipq806x: make use of ASCII env NVMEM driver for Linksys EAX devices

ipq806x: make use of ASCII env NVMEM driver for Linksys EAX devices

Make use of ASCII env NVMEM driver for Linksys EAX devices. This also
fix a problem with Linksys EAX devices where the 2 MAC interface had the
same MAC address causing a conflicts with FDB entry. This got much more
present with the DSA conversion making the system not usable.

To fix this, increment + 1 the MAC address for the WAN interface.

Link: https://github.com/openwrt/openwrt/pull/17839
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>