sunxi: Enable eMMC on Cubietruck Plus

Set CONFIG_MMC_SUNXI_SLOT_EXTRA=2 to enable the eMMC controller to
access eMMC on the board.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
diff --git a/configs/Cubietruck_plus_defconfig b/configs/Cubietruck_plus_defconfig
index 34444ec..3d999192 100644
--- a/configs/Cubietruck_plus_defconfig
+++ b/configs/Cubietruck_plus_defconfig
@@ -4,6 +4,7 @@
 CONFIG_DRAM_CLK=672
 CONFIG_DRAM_ZQ=15355
 CONFIG_DRAM_ODT_EN=y
+CONFIG_MMC_SUNXI_SLOT_EXTRA=2
 CONFIG_USB0_VBUS_PIN="AXP0-VBUS-ENABLE"
 CONFIG_USB0_VBUS_DET="AXP0-VBUS-DETECT"
 CONFIG_USB0_ID_DET="PH11"