greybus: kernel_ver: add list_last_entry for old kernels

Add list_last_entry macro for kernels older than 3.13.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>