sunxi: Move SUNXI_GMAC to Kconfig

Move the SUNXI_GMAC config option to Kconfig, remove it
from SYS_EXTRA_OPTIONS and rename it into SUN7I_GMAC.

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 8aa9279..1ba844d 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -161,6 +161,11 @@
 	  This driver supports Realtek 8169 series gigabit ethernet family of
 	  PCI/PCIe chipsets/adapters.
 
+config SUN7I_GMAC
+	bool "Enable Allwinner GMAC Ethernet support"
+	help
+	  Enable the support for Sun7i GMAC Ethernet controller
+
 config SUN8I_EMAC
         bool "Allwinner Sun8i Ethernet MAC support"
         depends on DM_ETH