Blackfin EMAC Driver: code cleanup

 - replace specific "bf537" function or data structure name to "bfin_mac"
 - cleanup bfin_mac_probe with error checking
 - punt set_pin_mux function, call peripheral request/free list functions directly

Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>