dma: move dma_ops to dma-uclass.h

Move dma_ops to a separate header file, following other uclass
implementations. While doing so, this patch also improves dma_ops
documentation.

Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
diff --git a/drivers/dma/ti-edma3.c b/drivers/dma/ti-edma3.c
index 2131e10..7e11b13 100644
--- a/drivers/dma/ti-edma3.c
+++ b/drivers/dma/ti-edma3.c
@@ -11,7 +11,7 @@
 #include <asm/io.h>
 #include <common.h>
 #include <dm.h>
-#include <dma.h>
+#include <dma-uclass.h>
 #include <asm/omap_common.h>
 #include <asm/ti-common/ti-edma3.h>