Rename rpi4b.conf to rpi.conf

[EvilOlaf]

Description

Since there is one generic config for all boards from 3b up to 5 and to avoid confusion, I suggested to rename board config file to rpi.

Though I don't know which parts depending on this file name need adjustments, like auto-builds in armbian/os or armbian/community and homepage entry.
All of that needs to be collected and addressed before or while merge.

Documentation summary for feature / change

How Has This Been Tested?

• None

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

[igorpecovnik]

We don't have upgrades of BSP in case of renames. The rest is not an issue I think.

[EvilOlaf]

Hm...what about this? create a symlink rpi.conf -> rpi4b.conf? Does the framework allow board config files which are actually symlinks rather than real files?