subsys/img_mgmt: Add zephyr/toolchain.h for STRINGIFY [v2]

Somehow two files in subsys/mgmt/mcumgr/lib/cmd/img_mgmt/src ended up
using STRINGIFY but nothing in their include path ended up pulling in
zephyr/toolchain/common.h. Include that via zephyr/toolchain.h.

v2:
	Use non-internal zephyr/toolchain.h header

Signed-off-by: Keith Packard <[email protected]>

Author: keith-packard

subsys/mgmt/mcumgr/lib/cmd/img_mgmt/src/img_mgmt.c

@@ -8,6 +8,7 @@
 #include <limits.h>
 #include <assert.h>
 #include <string.h>
+#include <zephyr/toolchain.h>
 
 #include <zcbor_common.h>
 #include <zcbor_decode.h>

subsys/mgmt/mcumgr/lib/cmd/img_mgmt/src/img_mgmt_state.c

@@ -6,6 +6,7 @@
 
 #include <assert.h>
 #include <zephyr/sys/util_macro.h>
+#include <zephyr/toolchain.h>
 
 #include <string.h>
 #include <zcbor_common.h>