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/configs/Hummingbird_A31_defconfig b/configs/Hummingbird_A31_defconfig
index c1cbbc8..d5de518 100644
--- a/configs/Hummingbird_A31_defconfig
+++ b/configs/Hummingbird_A31_defconfig
@@ -8,7 +8,7 @@
 CONFIG_VIDEO_VGA_EXTERNAL_DAC_EN="PH25"
 CONFIG_DEFAULT_DEVICE_TREE="sun6i-a31-hummingbird"
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
-CONFIG_SYS_EXTRA_OPTIONS="SUNXI_GMAC,RGMII"
+CONFIG_SYS_EXTRA_OPTIONS="RGMII"
 CONFIG_SPL=y
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_FLASH is not set
@@ -17,5 +17,6 @@
 # CONFIG_SPL_ISO_PARTITION is not set
 # CONFIG_SPL_EFI_PARTITION is not set
 CONFIG_ETH_DESIGNWARE=y
+CONFIG_SUN7I_GMAC=y
 CONFIG_AXP_ALDO1_VOLT=3300
 CONFIG_USB_EHCI_HCD=y