Preliminary Arch linux support for RockPro64

To install arch linux arm on a rockpro64:

1. Zero the first 32MB of the sd card:
   dd if=/dev/zero of=/dev/sdX bs=1M count=32

2. Use fdisk to partition the card:
   fdisk /dev/sdX
   At the fdisk prompt, create the new partition:

   a. Type o. This will clear out any partitions on the drive.
   b. Type p to list partitions. There should be no partitions left.
   c. Type n, then p for primary, 1 for the first partition on the drive, 32768 for the first sector, and then press ENTER to accept the default last sector.
   d. Write the partition table and exit by typing w.

3. Create ext4 filesystem
   mkfs.ext4 /dev/sdX1

4. Mount the filesystem

mkdir root
mount /dev/sdX1 root 

5. Download and extract the root filesystem

wget http://os.archlinuxarm.org/os/ArchLinuxARM-aarch64-latest.tar.gz
bsdtar -xpf ArchLinuxARM-aarch64-latest.tar.gz -C root

6. Place the attached boot.scr in root/boot/

7. Unmount the partition
   umount root

8. Write the bootloader to the sd card
   dd if=idbloader.img of=/dev/sdX seek=64 conv=notrunc

Then boot up the board with the sd card. The mainline aarch64 kernel is slow to boot and can take 3-5 minutes before the system is available through ssh.