check_config: add missing dependency check for MBEDTLS_PK_WRITE_C

MBEDTLS_PK_WRITE_C requires MBEDTLS_ASN1_WRITE_C, but there is no
corresponding check in check_config.h. In addition, corresponding
documentation for `Requires` is updated in mbedtls_config.h.

Signed-off-by: Yanray Wang <yanray.wang@arm.com>
diff --git a/include/mbedtls/check_config.h b/include/mbedtls/check_config.h
index 1ccd24e..576efea 100644
--- a/include/mbedtls/check_config.h
+++ b/include/mbedtls/check_config.h
@@ -440,7 +440,9 @@
 #endif
 
 #if defined(MBEDTLS_PK_WRITE_C) && \
-    (!defined(MBEDTLS_PK_C) || !defined(MBEDTLS_OID_C))
+    (!defined(MBEDTLS_ASN1_WRITE_C) || \
+     !defined(MBEDTLS_OID_C)        || \
+     !defined(MBEDTLS_PK_C))
 #error "MBEDTLS_PK_WRITE_C defined, but not all prerequisites"
 #endif
 
diff --git a/include/mbedtls/mbedtls_config.h b/include/mbedtls/mbedtls_config.h
index 2cfb4fc..254e75a 100644
--- a/include/mbedtls/mbedtls_config.h
+++ b/include/mbedtls/mbedtls_config.h
@@ -3073,7 +3073,7 @@
  * Module:  library/pkwrite.c
  * Caller:  library/x509write.c
  *
- * Requires: MBEDTLS_PK_C, MBEDTLS_OID_C
+ * Requires: MBEDTLS_ASN1_WRITE_C, MBEDTLS_OID_C, MBEDTLS_PK_C
  *
  * Uncomment to enable generic public key write functions.
  */