Declare a psa_key_file_id_t layout with an owner field

Declare the owner as psa_key_owner_id_t, of which an implementation
must be provided separately.

Make this a configuration option
MBEDTLS_PSA_CRYPTO_KEY_FILE_ID_ENCODES_OWNER, to make the conditional
compilation flow easier to follow. Declare it in config.h to
pacify check_names.sh.

Support for a specific implementation of psa_key_owner_id_t in storage
backends will come in a subsequent commit.
diff --git a/scripts/config.pl b/scripts/config.pl
index 55f4b6e..e141b41 100755
--- a/scripts/config.pl
+++ b/scripts/config.pl
@@ -100,6 +100,7 @@
 MBEDTLS_NO_64BIT_MULTIPLICATION
 MBEDTLS_PSA_CRYPTO_SPM
 MBEDTLS_PSA_HAS_ITS_IO
+MBEDTLS_PSA_CRYPTO_KEY_FILE_ID_ENCODES_OWNER
 MBEDTLS_PSA_CRYPTO_STORAGE_ITS_C
 MBEDTLS_USE_PSA_CRYPTO
 _ALT\s*$