omap4: sdma: Enable the idle modes on omap4

This patch enables smart-idle idlemodes and autoidle for sDMA
on OMAP4

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Reviewed-by: Kevin Hilman <khilman@deeprootsystems.com>
Reviewed-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>