net: move Broadcom SF2 driver to Kconfig

move to Kconfig:
	CONFIG_BCM_SF2_ETH
	CONFIG_BCM_SF2_ETH_DEFAULT_PORT
	CONFIG_BCM_SF2_ETH_GMAC

Also modified defconfigs of all platforms that use these configs.

Signed-off-by: Suji Velupillai <suji.velupillai@broadcom.com>
Tested-by: Suji Velupillai <suji.velupillai@broadcom.com>
Reviewed-by: JD Zheng <jiandong.zheng@broadcom.com>
Reviewed-by: Scott Branden <scott.branden@broadcom.com>
Signed-off-by: Steve Rae <steve.rae@raedomain.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 7f6ab4a..9cfeede 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -523,6 +523,9 @@
 	imply CMD_HASH
 	imply FAT_WRITE
 	imply HASH_VERIFY
+	imply NETDEVICES
+	imply BCM_SF2_ETH
+	imply BCM_SF2_ETH_GMAC
 
 config TARGET_BCMNSP
 	bool "Support bcmnsp"