ath79: ja76pf2: use nvmem cells to specify MAC addresses

ath79: ja76pf2: use nvmem cells to specify MAC addresses

The bootloader on this board hid the partition containig MAC addresses
and prevented adding this space to FIS directory, therefore those had to
be stored in RedBoot configuration as aliases to be able to assigne them
to proper interfaces. Now that fixed partition size are used instead of
redboot-fis parser, the partition containig MAC addresses could be
specified, and with marking it as nvmem cell, we can assign them without
userspace involvement.

Signed-off-by: Tomasz Maciej Nowak <tmn505@gmail.com>
(cherry picked from commit b52719b71a3337e5ae840c7a50fe41ebdc070f4e)