string: ensure string included when used

Latest upstream yocto appears to have removed a free include of string.
This is causing compile failures for files which do not include it
properly.

Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: I8df4c564af2c8e8294cdcb3e74f9d7cd106d4ec8
4 files changed