mbed: Add CMake support and fix files paths

The mbed port should be compatible with a new command-line tool
mbed-tools (Mbed CLI 2) which use cmake build system. This allows build
cmake-base applications.
Fix mbed files paths - it's required for the new version of mbed-os
(v6.15)

Signed-off-by: Artur Tynecki <artur.tynecki@mobica.com>
diff --git a/boot/mbed/mcuboot_main.cpp b/boot/mbed/mcuboot_main.cpp
index c5f4137..4acb34d 100644
--- a/boot/mbed/mcuboot_main.cpp
+++ b/boot/mbed/mcuboot_main.cpp
@@ -22,7 +22,7 @@
 #include "bootutil/bootutil.h"
 #include "bootutil/image.h"
 #include "hal/serial_api.h"
-#include "mbed_application.h"
+#include "platform/mbed_application.h"
 
 #if (MCUBOOT_CRYPTO_BACKEND == MBEDTLS)
 #include "mbedtls/platform.h"