patch: make SD images for arm64 boards at same release.sh

[YAMAMOTO Shigeru]

Hi, all,

I try to change src/release/release.sh to make SD images for
RPI3/PINE64/PINE64-LTE/PINEBOOK.

diff for head is
https://github.com/bsd-hacker/freebsd/pull/3

A sequence of making a SD image is
1. make cross compile environment
2. make user land binarys
3. make kernel
4. install user land binarys to a SD image
5. install kernel to a SD image
6. install ipl/u-boot to a SD image
7. configure /etc

For RPI3/PINE64/PINE64-LTE/PINEBOOK, there is no differences without step 6.
So I change step 6 to loop for each boards.

I test RPI3, PINE64.
I can boot using RPI3 and PINE64 SD image.

I don't test PINE64-LTE, PINEBOOK because I have no them.

Thanks,
---
YAMAMOTO Shigeru <shigeru at os-hackers.jp>