pico-imx6ul: Add fastboot support

fastboot tool is a convenient way to flash the eMMC, so
add support for it.

Examples of usages:

On the pico-imx6ul U-Boot prompt:

=> fastboot 0

On the Linux PC connected via USB:

1. Retrieving the U-Boot version

$ sudo fastboot getvar bootloader-version -i 0x0525
bootloader-version: U-Boot 2018.07-rc2-00130-g0881835-dirty
finished. total time: 0.000s

2. Resetting the board

$ sudo fastboot reboot -i 0x0525

(this causes the pico-imx6ul to reboot)

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Fabio Berton <fabio.berton@ossystems.com.br>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
diff --git a/configs/pico-imx6ul_defconfig b/configs/pico-imx6ul_defconfig
index 589e67b..cae7ded 100644
--- a/configs/pico-imx6ul_defconfig
+++ b/configs/pico-imx6ul_defconfig
@@ -45,6 +45,12 @@
 CONFIG_CMD_FS_GENERIC=y
 CONFIG_ENV_IS_IN_MMC=y
 CONFIG_DFU_MMC=y
+CONFIG_USB_FUNCTION_FASTBOOT=y
+CONFIG_FASTBOOT_BUF_ADDR=0x82000000
+CONFIG_FASTBOOT_BUF_SIZE=0x10000000
+CONFIG_FASTBOOT_FLASH=y
+CONFIG_FASTBOOT_FLASH_MMC_DEV=0
+CONFIG_FASTBOOT_CMD_OEM_FORMAT=y
 CONFIG_FSL_ESDHC=y
 CONFIG_PHYLIB=y
 CONFIG_PHY_MICREL=y
@@ -56,5 +62,4 @@
 CONFIG_USB_GADGET_VENDOR_NUM=0x0525
 CONFIG_USB_GADGET_PRODUCT_NUM=0xa4a5
 CONFIG_CI_UDC=y
-CONFIG_USB_GADGET_DOWNLOAD=y
 CONFIG_OF_LIBFDT=y