Build: Update MCUboot version

Pick-up a version which contains all features
which were upstreamed from TF-M MCUboot fork.

Change-Id: Ic59069c8851cf003133124838365ae97abc389ba
Signed-off-by: Tamas Ban <tamas.ban@arm.com>
diff --git a/config/config_default.cmake b/config/config_default.cmake
index a5ca8cc..f25d35c 100644
--- a/config/config_default.cmake
+++ b/config/config_default.cmake
@@ -125,7 +125,7 @@
 set(CMSIS_5_PATH                        "DOWNLOAD"  CACHE PATH      "Path to CMSIS_5 (or DOWNLOAD to fetch automatically")
 
 set(MCUBOOT_PATH                        "DOWNLOAD"  CACHE PATH      "Path to MCUboot (or DOWNLOAD to fetch automatically")
-set(MCUBOOT_VERSION                     "v1.6.0"    CACHE STRING    "The version of MCUboot to use")
+set(MCUBOOT_VERSION                     "b2a1a48"   CACHE STRING    "The version of MCUboot to use")
 set(TFM_INTERNAL_MCUBOOT                OFF         CACHE BOOL      "Use internal MCUboot files instead of upstream repo")
 
 set(PSA_ARCH_TESTS_PATH                 "DOWNLOAD"  CACHE PATH      "Path to PSA arch tests (or DOWNLOAD to fetch automatically")