Switch library and tests to the x509_oid module

```
git grep -l -P 'mbedtls_oid_get_(?!numeric_string\b)' | xargs perl -i -pe 's/\bmbedtls_oid_get_(?!numeric_string\b)/mbedtls_x509_oid_get_/'
./framework/scripts/code_style.py --since HEAD~1 --fix
```

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/pkcs7.c b/library/pkcs7.c
index 3c5040b..cfe570a 100644
--- a/library/pkcs7.c
+++ b/library/pkcs7.c
@@ -480,7 +480,7 @@
         return ret;
     }
 
-    ret = mbedtls_oid_get_md_alg(&signed_data->digest_alg_identifiers, &md_alg);
+    ret = mbedtls_x509_oid_get_md_alg(&signed_data->digest_alg_identifiers, &md_alg);
     if (ret != 0) {
         return MBEDTLS_ERR_PKCS7_INVALID_ALG;
     }
@@ -659,7 +659,7 @@
         return MBEDTLS_ERR_PKCS7_CERT_DATE_INVALID;
     }
 
-    ret = mbedtls_oid_get_md_alg(&pkcs7->signed_data.digest_alg_identifiers, &md_alg);
+    ret = mbedtls_x509_oid_get_md_alg(&pkcs7->signed_data.digest_alg_identifiers, &md_alg);
     if (ret != 0) {
         return ret;
     }