pico-imx6ul: Add boot and rootfs dfu_alt_info

pico-imx6ul: Add boot and rootfs dfu_alt_info

Change dfu_alt_info variable to use the following altsetting:

  uboot:                     To flash raw U-Boot
  /zImage: boot:             To copy kernel image
  /imx6ul-pico-hobbit.dtb:   To copy dtb file
  rootfs:                    To copy rootfs

List the currently attached DFU capable USB devices running:
  sudo dfu-util -l

Flash U-Boot:
  sudo dfu-util -D u-boot.imx -a uboot

Copy boot files:
  sudo dfu-util -D zImage -a /zImage
  sudo dfu-util -D imx6ul-pico-hobbit.dtb -a /imx6ul-pico-hobbit.dtb

Flash rootfs:
  sudo dfu-util -D rootfs.ext4 -a rootfs

To copy boot files you need to have a formated mmc 0:1 partition. To
format with ext4 filesystem you can use ums.

Run on target:
  ums 0 mmc 0

and on host:
  sudo mkfs.ext4 /dev/sdx1

Signed-off-by: Fabio Berton <fabio.berton@ossystems.com.br>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>