Boot: Sync MCUBoot code base

This patch performs a partial synchronization between the MCUBoot files
in TF-M and in the original repository. The hash of the source commit
in the original MCUBoot repo: 3c469bc698a9767859ed73cd0201c44161204d5c.

Change-Id: I244b47f21ebdfc73381accc007ee88737f7ccdf7
Signed-off-by: David Vincze <david.vincze@arm.com>
diff --git a/bl2/ext/mcuboot/bootutil/src/image_rsa.c b/bl2/ext/mcuboot/bootutil/src/image_rsa.c
index a9f2393..22dc6e3 100644
--- a/bl2/ext/mcuboot/bootutil/src/image_rsa.c
+++ b/bl2/ext/mcuboot/bootutil/src/image_rsa.c
@@ -20,7 +20,7 @@
 /*
  * Original code taken from mcuboot project at:
  * https://github.com/JuulLabs-OSS/mcuboot
- * Git SHA of the original version: 178be54bd6e5f035cc60e98205535682acd26e64
+ * Git SHA of the original version: 3c469bc698a9767859ed73cd0201c44161204d5c
  * Modifications are Copyright (c) 2018-2019 Arm Limited.
  */