ath79: calibrate dlink dir-825 c1 and dir-835 a1 with nvmem

ath79: calibrate dlink dir-825 c1 and dir-835 a1 with nvmem

Driver for both soc (2.4GHz Wifi) and pci (5 GHz) now pull the calibration
data from the nvmem subsystem.

This allows us to move the userspace caldata extraction for the pci-e ath9k
supported wifi into the device-tree definition of the device.

Currently, "mac-address-ascii" cells only works for ethernet and wmac devices,
so PCI ath9k device uses the old method to calibrate.

Signed-off-by: Edward Chow <equu@openmail.cc>