net: thunderx: bgx: Use standard firmware node infrastructure.

net: thunderx: bgx: Use standard firmware node infrastructure.

In the case of OF device tree, the firmware information is attached to
the BGX device structure in the standard manner, so use the firmware
iterators and accessors where possible.

Signed-off-by: David Daney <david.daney@cavium.com>
Signed-off-by: Sunil Goutham <sgoutham@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from linux-next commit eee326fd83348ed39a06c0db999ed513d10d9c39)
Signed-off-by: Dann Frazier <dann.frazier@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>