Mbed TLS importer: Call `config.pl --force` to accept unknown option

The new PSA-aware Mbed TLS importer script calls `config.pl` on the
Mbed TLS config.h to set the PSA configuration option
MBEDTLS_PSA_CRYPTO_STORAGE_C which isn't documented in config.h.
config.pl therefore fails, and so does the importer.

This commit fixes this by calling `config.pl` with the `--force`
option which amends the given `config.h` by a `#define` for the
requested option if the option isn't present in the file.

features/mbedtls/importer/adjust-config.sh

@@ -22,7 +22,7 @@ SCRIPT=$1
 FILE=$2
 
 conf() {
-    $SCRIPT -f $FILE $@
+    $SCRIPT -f $FILE --force $@
 }
 
 add_code() {