dmaengine: mmp_tdma: Allow building as a module

There is no reason the Marvell MMP two-channel audio DMA driver would have
to be built-in.
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Link: https://lore.kernel.org/r/20210121110356.1768635-4-lkundrak@v3.skSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/Kconfig

@@ -378,7 +378,7 @@ config MMP_PDMA
 	  Support the MMP PDMA engine for PXA and MMP platform.
 
 config MMP_TDMA
-	bool "MMP Two-Channel DMA support"
+	tristate "MMP Two-Channel DMA support"
 	depends on ARCH_MMP || COMPILE_TEST
 	select DMA_ENGINE
 	select GENERIC_ALLOCATOR