serial: 8250: Add support for dmaengine

Add support for dmaengine API. The drivers can implement the
struct uart_8250_dma member in struct uart_8250_port and
8250.c can take care of the rest.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/serial_8250.h

@@ -59,6 +59,8 @@ enum {
 	PLAT8250_DEV_SM501,
 };
 
+struct uart_8250_dma;
+
 /*
  * This should be used by drivers which want to register
  * their own 8250 ports without registering their own
@@ -91,6 +93,8 @@ struct uart_8250_port {
 #define MSR_SAVE_FLAGS UART_MSR_ANY_DELTA
 	unsigned char		msr_saved_flags;
 
+	struct uart_8250_dma	*dma;
+
 	/* 8250 specific callbacks */
 	int			(*dl_read)(struct uart_8250_port *);
 	void			(*dl_write)(struct uart_8250_port *, int);