test: dma: add dma-uclass test

Add a sandbox DMA driver implementation (provider) and corresponding DM
test.

Reviewed-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Álvaro Fernández Rojas <noltari@gmail.com>
diff --git a/drivers/dma/Kconfig b/drivers/dma/Kconfig
index b9b85c6..8a4162e 100644
--- a/drivers/dma/Kconfig
+++ b/drivers/dma/Kconfig
@@ -19,6 +19,13 @@
 	  Enable channels support for DMA. Some DMA controllers have multiple
 	  channels which can either transfer data to/from different devices.
 
+config SANDBOX_DMA
+	bool "Enable the sandbox DMA test driver"
+	depends on DMA && DMA_CHANNELS && SANDBOX
+	help
+	  Enable support for a test DMA uclass implementation. It stimulates
+	  DMA transfer by simple copying data between channels.
+
 config TI_EDMA3
 	bool "TI EDMA3 driver"
 	help