Convert CONFIG_SYS_UNIFY_CACHE to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_UNIFY_CACHE

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 40b5c82..cb891f5 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -409,6 +409,10 @@
 	  This driver supports the network interface units in the
 	  ColdFire family.
 
+config SYS_UNIFY_CACHE
+	depends on MCFFEC
+	bool "Invalidate icache during ethernet operations"
+
 config FSLDMAFEC
         bool "ColdFire DMA Ethernet Support"
 	depends on DM_ETH