This is for the below configuration:
Distro: Archlinuxarm
Requestor: SnowWhite
SDcard: Archlinuxarm
USB drive: Archlinuxarm

If USB drive has ArchLinuxArm, boot it (will only work if its /dev/sda1)
If USB drive not present then boot ArchLinuxArm in SD card.

Steps:
1. Install distro in SD card:
   Will get /dev/mmcblk0p1 (VFAT) and /dev/mmcblk0p2 (rootfs)
2. Create 1st partition as ext4 in USB drive. Copy ArchlinuxARM rootfs in 
   the USB drive.
3. Edit /etc/fstab in both SD card and USB drive andn comment out /boot mount.
4. Copy boot.txt and boot.scr present in the boot directory to VFAT (mmcblk0p1)
   partition of SD card.
5. Fuse new u-boot to SD card (by running ./sd_fusing.sh /dev/<SD card device>)
   Example: ./sd_fusing.sh /dev/mmcblk0
6. Plug SD card in Odroid and power on.

