add a CFGDB_SCHEMA setting to the make process

[pljakobs]

currently, the build process just processes all .cfgdb files in the project directory.
To be more in line with how HWCONFIG is handled, I suggest that we add a setting to select a specific .cfgdb file.
afaiu, using "include" within the .configdb file, we can still create multi-file configurations.

[mikee47]

Not quite the same as there can only be one hardware config for an application, whilst there can be multiple databases. If the application has multiple configurations, why would they only want to build one of them? What are the use-cases?

[pljakobs]

ok. my "Denkfehler" as we say - "fallacy on thinking" seems to be the English term. disregard, please, you're right.

[mikee47]

Another wonderful word! I shall have to work that one into conversation - thank you!