The #include has been splattered all over the place, but there are
precious few places, all .c files, that actually need it.

v2: remove leftover double newlines
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200225133131.3301-1-jani.nikula@intel.com