dmaengine: mmp_pdma: Allow building as a module

There is no reason the Marvell MMP peripheral DMA driver would have
to be built-in.
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Link: https://lore.kernel.org/r/20210121110356.1768635-3-lkundrak@v3.skSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/Kconfig

@@ -371,7 +371,7 @@ config MILBEAUT_XDMAC
 	  XDMAC device.
 
 config MMP_PDMA
-	bool "MMP PDMA support"
+	tristate "MMP PDMA support"
 	depends on ARCH_MMP || ARCH_PXA || COMPILE_TEST
 	select DMA_ENGINE
 	help