feat(libfdt): add function to set MAC addresses

The devicetree specification[1] defines the generic DT properties
"mac-address" and "local-mac-address", that allow to set the MAC address
for a network device. This is needed because many platform network
devices do not define a method for obtaining a unique MAC address, and
many devices lack the non-volatile storage to hold such a number.

Some platforms (for instance Allwinner) derive the MAC address from
another unique SoC property, for instance some serial number. To allow
those MAC address to be set by TF-A, add a function that finds the DT
node of a network device (by using the "ethernet<x>" alias), then adding
the "local-mac-address" property into that node, setting it to a user
provided address. Platforms can use this function to generate MAC
addresses in a platform specific way, and store them in the DT.

DT consumers like U-Boot or the Linux kernel will automatically pick up
the address from that property and program the MAC device accordingly.

[1] https://devicetree-specification.readthedocs.io/en/latest/chapter4-device-bindings.html#local-mac-address-property

Change-Id: I3f5766cc575fa9718f9ca23e8269b11495c43be2
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
2 files changed