ath79: convert TP-Link Archer C7v1/2 Wifis to nvmem-cells

ath79: convert TP-Link Archer C7v1/2 Wifis to nvmem-cells

For v2, both ath9k (2.4GHz Wifi) and ath10k (5 GHz) driver now
pull the (pre-)calibration data from the nvmem subsystem. v1
is slightly different as only the ath9k Wifi is supported.

This allows us to move the userspace caldata extraction
and mac-address patching for the 5GHZ ath10k supported
wifi into the device-tree definition of the device.

ath9k's nodes are also changed over to use nvmem-cells
over OpenWrt's custom mtd-cal-data property.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>