greybus: camera: Add wrapper for sync operation with flags

The greybus operation core synchronous operation call doesn't support
operation flags. Create a new synchronous operation wrapper with flags,
and modify the capabilities operation implementation to use it.

The code could be later moved to the greybus core if other drivers have
a similar need.

Signed-off-by: Jacopo Mondi <jacopo.mondi@linaro.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>