sunxi: Convert SUNXI_EMAC to Kconfig

Convert the SUNXI_EMAC config to Kconfig. Remove it from SYS_EXTRA_OPTIONS
from many sunxi defconfig and renamed it into SUN4I_EMAC to not confuse it
with SUN8I_EMAC.

Signed-off-by: Mylène Josserand <mylene.josserand@free-electrons.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 1ba844d..6126d10 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -166,6 +166,12 @@
 	help
 	  Enable the support for Sun7i GMAC Ethernet controller
 
+config SUN4I_EMAC
+	bool "Allwinner Sun4i Ethernet MAC support"
+	depends on DM_ETH
+	help
+	  This driver supports the Allwinner based SUN4I Ethernet MAC.
+
 config SUN8I_EMAC
         bool "Allwinner Sun8i Ethernet MAC support"
         depends on DM_ETH