mac802154: add support for perm_extended_addr

This patch adding support for a perm extended address. This is useful
when a device supports an eeprom with a programmed static extended address.
If a device doesn't support such eeprom or serial registers then the
driver should generate a random extended address.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>