net/Blackfin: move on-chip MAC driver into drivers/net/

The Blackfin on-chip MAC driver was being managed in the BF537-STAMP board
directory, but it is not board specific, so relocate it to the drivers dir
so that other Blackfin ports can utilize it.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/drivers/net/Makefile b/drivers/net/Makefile
index b9723fa..321bd08 100644
--- a/drivers/net/Makefile
+++ b/drivers/net/Makefile
@@ -27,6 +27,7 @@
 
 COBJS-y += 3c589.o
 COBJS-y += bcm570x.o bcm570x_autoneg.o 5701rls.o
+COBJS-$(CONFIG_BFIN_MAC) += bfin_mac.o
 COBJS-y += cs8900.o
 COBJS-y += dc2114x.o
 COBJS-y += dm9000x.o