use gpt partition table on rock-3a

[amazingfate]

Description

As the issue @catalinii mentioned in #3271, when a sdcard has got flashed with radxa rock3a image or manjaro-arm rock3a image before, armbian can't boot on this sd card after flashed with ether. Here is the root cause: https://forum.armbian.com/topic/12352-orange-pi-4/page/3/#comment-94322.
We can avoid this issue by using the same gpt partition type as radxa and manjaro, and use the same fat /boot partition to aviod the bad support for ext4 filesystem from rockchip legacy u-boot.

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Please also note any relevant details for your test configuration.

• Prepare a sd card, flash it with radxa official image, and then flash the armbian image built before this commit, the sd card failed to boot.
• Flash the sd card with armbian image built with this commit, system boots up successfully.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

[catalinii]

Thanks @amazingfate

[vukitoso]

Thx, works.