dmaengine: mediatek: Add MediaTek UART APDMA support

Add 8250 UART APDMA to support MediaTek UART. If MediaTek UART is
enabled by SERIAL_8250_MT6577, and we can enable this driver to offload
the UART device moving bytes.
Signed-off-by: Long Cheng <long.cheng@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/mediatek/Kconfig

@@ -24,3 +24,14 @@ config MTK_CQDMA
 
 	  This controller provides the channels which is dedicated to
 	  memory-to-memory transfer to offload from CPU.
+
+config MTK_UART_APDMA
+	tristate "MediaTek SoCs APDMA support for UART"
+	depends on OF && SERIAL_8250_MT6577
+	select DMA_ENGINE
+	select DMA_VIRTUAL_CHANNELS
+	help
+	  Support for the UART DMA engine found on MediaTek MTK SoCs.
+	  When SERIAL_8250_MT6577 is enabled, and if you want to use DMA,
+	  you can enable the config. The DMA engine can only be used
+	  with MediaTek SoCs.

drivers/dma/mediatek/Makefile

+obj-$(CONFIG_MTK_UART_APDMA) += mtk-uart-apdma.o
 obj-$(CONFIG_MTK_HSDMA) += mtk-hsdma.o
 obj-$(CONFIG_MTK_CQDMA) += mtk-cqdma.o