local_t: Move local.h include to ringbuffer.c and ring_buffer_benchmark.c

ringbuffer*.c are the last users of local.h.

Remove the include from modules.h and add it to ringbuffer files.

Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Tejun Heo <tj@kernel.org>