gianfar: Move tbase/rbase initialization to gfar_init_mac()

For hibernation we want to call gfar_init_mac() without need to
free/allocate_skb_resources sequence, so save the DMA address into a
private struct, and move tbase/rbase initialization to gfar_init_mac().

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>