Convert CONFIG_SUPPORT_EMMC_BOOT to Kconfig

This converts the following to Kconfig:
	CONFIG_SUPPORT_EMMC_BOOT

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/apalis-imx8x_defconfig b/configs/apalis-imx8x_defconfig
index d197ad9..2cd91e1 100644
--- a/configs/apalis-imx8x_defconfig
+++ b/configs/apalis-imx8x_defconfig
@@ -53,6 +53,7 @@
 CONFIG_I2C_MUX=y
 CONFIG_I2C_MUX_PCA954x=y
 CONFIG_MISC=y
+CONFIG_SUPPORT_EMMC_BOOT=y
 CONFIG_FSL_USDHC=y
 CONFIG_PHYLIB=y
 CONFIG_PHY_ADDR_ENABLE=y