[S] Change in flashrom[master]: Hook up mjson into build system

[Edward O'Callaghan (Code Review)]

Attention is currently required from: Stefan Reinauer, Thomas Heijligen.

Edward O'Callaghan has posted comments on this change. ( https://review.coreboot.org/c/flashrom/+/75648?usp=email )

Change subject: Hook up mjson into build system
......................................................................

Patch Set 5: Code-Review+1

(1 comment)

File meson.build:

https://review.coreboot.org/c/flashrom/+/75648/comment/595dadf1_8898f228 :
PS5, Line 76:   'mjson.c',
            :   'flashchips.c',
probably the structure should be:

```
imports/mjson/{mjson.c, meson.build} => gen 'mjson.a'.
```

&&

```
flashchipdb/{flashchips.c, flashchips.h, meson.build} => gen flashchips.a
```

this affords us the path to having a feature flag for link-time decision to which db to use - builtin or parsed external. WDYT?