check_config: combine check for MBEDTLS_PK_PARSE_C

- check_config.h: combine separate check for MBEDTLS_PK_PARSE_C
- mbedtls_config.h: update documentation for `Requires`

Signed-off-by: Yanray Wang <yanray.wang@arm.com>
diff --git a/include/mbedtls/mbedtls_config.h b/include/mbedtls/mbedtls_config.h
index edf4a0b..2cfb4fc 100644
--- a/include/mbedtls/mbedtls_config.h
+++ b/include/mbedtls/mbedtls_config.h
@@ -3059,7 +3059,7 @@
  * Caller:  library/x509_crt.c
  *          library/x509_csr.c
  *
- * Requires: MBEDTLS_PK_C, MBEDTLS_OID_C
+ * Requires: MBEDTLS_ASN1_PARSE_C, MBEDTLS_OID_C, MBEDTLS_PK_C
  *
  * Uncomment to enable generic public key parse functions.
  */