dmaengine: tegra-apb: Allow to compile as a loadable kernel module

The driver's removal was fixed by a recent commit and module load/unload
is working well now, tested on Tegra30.
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Link: https://lore.kernel.org/r/20200209163356.6439-16-digetx@gmail.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/Kconfig

@@ -616,7 +616,7 @@ config TXX9_DMAC
 	  integrated in chips such as the Toshiba TX4927/38/39.
 
 config TEGRA20_APB_DMA
-	bool "NVIDIA Tegra20 APB DMA support"
+	tristate "NVIDIA Tegra20 APB DMA support"
 	depends on ARCH_TEGRA
 	select DMA_ENGINE
 	help