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: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>

configs/Cubietruck_plus_defconfig

@@ -4,6 +4,7 @@ CONFIG_MACH_SUN8I_A83T=y
 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"