tty: serial: msm: Add TX DMA support

Add transmit DMA support for UARTDM type of controllers.

Tested on APQ8064, which have UARTDM v1.3 and ADM DMA engine
and APQ8016, which have UARTDM v1.4 and BAM DMA engine.

Signed-off-by: Ivan T. Ivanov <ivan.ivanov@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/msm_serial.h

@@ -121,6 +121,9 @@
 #define UARTDM_DMEN_RX_SC_ENABLE BIT(5)
 #define UARTDM_DMEN_TX_SC_ENABLE BIT(4)
 
+#define UARTDM_DMEN_TX_BAM_ENABLE BIT(2)	/* UARTDM_1P4 */
+#define UARTDM_DMEN_TX_DM_ENABLE  BIT(0)	/* < UARTDM_1P4 */
+
 #define UARTDM_DMRX		0x34
 #define UARTDM_NCF_TX		0x40
 #define UARTDM_RX_TOTAL_SNAP	0x38