src: Add missing <cbmem.h>

Change-Id: I75a816c594b326df8a4aa5458bb055fca35e1741
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50379
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>

src/include/imd_private.h

@@ -1,6 +1,7 @@
 #ifndef _IMD_PRIVATE_H_
 #define _IMD_PRIVATE_H_
 
+#include <cbmem.h>
 #include <commonlib/bsd/helpers.h>
 
 /* In-memory data structures. */