Radxa rock-3a - edge - add overlay to disable debug console

[mr-toolcraft]

Description

This adds a small overlay to allow the debug serial console being disabled. This will make two additional GPIO pins available for other purpose. Some people may need the additional I/O for whatever reason.

GitHub issue reference:
Jira reference number [AR-9999]

How Has This Been Tested?

• compile .dtso file using dtc
• enable and reboot: serial console is disabled
• compile ./compile.sh kernel BOARD=rock-3a BRANCH=edge KERNEL_CONFIGURE=no

Checklist:

Please delete options that are not relevant.

• 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
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

[EvilOlaf]

I don't think this needs much of a review. Overlay is disabled by default and I assume it'll be rarely used at all.

Though I won't approve my own stuff.