Any config with a version older than 3.0.0 or newer than
MBETLS_VERSION_NUMBER will be rejected.
This does mean that the current development version doesn'T accept *any*
value of MBETLS_CONFIG_VERSION, but this will be fixed when we bump the
version during our normal release process.
Signed-off-by: Bence Szépkúti <bence.szepkuti@arm.com>