tools: require at least json-c 0.15

If not available, fallback to using YAJL.

The code is using json_c_visit() which was introduced in 0.13.
json_object_new_null() and json_object_new_uint64() where added to
0.14. And the last one json_object_new_array_ext() was introduced in
0.15.

Signed-off-by: Anthony PERARD <anthony.perard@vates.tech>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Acked-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>

CHANGELOG.md

@@ -14,8 +14,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
  - Debian Trixie added to CI.  Debian Bullseye retired from CI for RISC-V due
    to the baseline change.
  - Linux based device model stubdomains are now fully supported.
- - New dependency on library json-c, the toolstack will prefer it to `YAJL`
-   when available.
+ - New dependency on library json-c 0.15 or later, the toolstack will prefer it
+   to `YAJL` when available.
 
  - On x86:
    - Restrict the cache flushing done as a result of guest physical memory map