Add support the Korina (IDT RC32434) Ethernet MAC

This patch adds support for the IDT rc32434 Ethernet MAC
we can find in the IDT boards and the Mikrotik RB500.
Driver references some code from the linux-mips RB500
support.

Signed-off-by: Florian Fainelli <florian.fainelli@telecomint.eu>
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Philip Rischel <rischelp@idt.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>