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/pico-imx6_defconfig b/configs/pico-imx6_defconfig
index 3f3fa01..2bd2203 100644
--- a/configs/pico-imx6_defconfig
+++ b/configs/pico-imx6_defconfig
@@ -64,6 +64,7 @@
 CONFIG_FASTBOOT_BUF_SIZE=0x10000000
 CONFIG_FASTBOOT_FLASH=y
 CONFIG_FASTBOOT_FLASH_MMC_DEV=0
+CONFIG_SUPPORT_EMMC_BOOT=y
 CONFIG_FSL_USDHC=y
 CONFIG_PHYLIB=y
 CONFIG_PHY_ATHEROS=y