FWU: Optimize the RAM cost in FWU partition

- Make PSA_FWU_MAX_BLOCK_SIZE and internal buf for block write
configurable.
- Decrease the stack size of FWU partition to a reasonable
value.

Signed-off-by: Sherry Zhang <sherry.zhang2@arm.com>
Change-Id: I8aa115d7824bf887b4fe0814c4bdb1dfd3407ce7
diff --git a/interface/include/psa/update.h b/interface/include/psa/update.h
index d7de5ac..5af0f1c 100644
--- a/interface/include/psa/update.h
+++ b/interface/include/psa/update.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, Arm Limited. All rights reserved.
+ * Copyright (c) 2021-2022, Arm Limited. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  *
@@ -12,13 +12,13 @@
 #include <stdint.h>
 
 #include "psa/error.h"
+#include "psa/fwu_config.h"
 #include "tfm_fwu_defs.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#define PSA_FWU_MAX_BLOCK_SIZE               1024
 #define TFM_FWU_INVALID_IMAGE_ID             0
 
 /* The maximum size of an image digest in bytes. This is dependent