of/net: Move of_get_mac_address() to a common source file.

There are two identical implementations of of_get_mac_address(), one
each in arch/powerpc/kernel/prom_parse.c and
arch/microblaze/kernel/prom_parse.c.  Move this function to a new
common file of_net.{c,h} and adjust all the callers to include the new
header.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
[grant.likely@secretlab.ca: protect header with #ifdef]
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
diff --git a/drivers/of/Makefile b/drivers/of/Makefile
index 7888155..3ab21a0 100644
--- a/drivers/of/Makefile
+++ b/drivers/of/Makefile
@@ -6,5 +6,6 @@
 obj-$(CONFIG_OF_DEVICE) += device.o platform.o
 obj-$(CONFIG_OF_GPIO)   += gpio.o
 obj-$(CONFIG_OF_I2C)	+= of_i2c.o
+obj-$(CONFIG_OF_NET)	+= of_net.o
 obj-$(CONFIG_OF_SPI)	+= of_spi.o
 obj-$(CONFIG_OF_MDIO)	+= of_mdio.o