[media] omap3isp: stat: Rename IS_COHERENT_BUF to ISP_STAT_USES_DMAENGINE

The macro is meant to test whether the statistics engine uses an
external DMA engine to transfer data or supports DMA directly. As both
cases will be supported by DMA coherent buffers rename the macro to
ISP_STAT_USES_DMAENGINE for improved clarity.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>