serial: 8250_lpss: Enable DMA on Intel Elkhart Lake

PSE UARTs on Intel Elkhart Lake support DMA mode.
Enable DMA on these ports.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210721162452.48764-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_lpss.c

@@ -158,6 +158,16 @@ static int byt_serial_setup(struct lpss8250 *lpss, struct uart_port *port)
 
 static int ehl_serial_setup(struct lpss8250 *lpss, struct uart_port *port)
 {
+	struct uart_8250_dma *dma = &lpss->data.dma;
+	struct uart_8250_port *up = up_to_u8250p(port);
+
+	/*
+	 * This simply makes the checks in the 8250_port to try the DMA
+	 * channel request which in turn uses the magic of ACPI tables
+	 * parsing (see drivers/dma/acpi-dma.c for the details) and
+	 * matching with the registered General Purpose DMA controllers.
+	 */
+	up->dma = dma;
 	return 0;
 }