serial: 8250_lpss: Add ->setup() for Elkhart Lake ports

The ->setup() callback is mandatory for the devices.
Provide it for Elkhart Lake UART ports.

Note, for time being it's empty, but in the future it might require
an additional configuration such as DMA.
Reported-by: NRaymond Tan <raymond.tan@intel.com>
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200305130822.36850-1-andriy.shevchenko@linux.intel.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -156,6 +156,11 @@ static int byt_serial_setup(struct lpss8250 *lpss, struct uart_port *port)
 	return 0;
 }
 
+static int ehl_serial_setup(struct lpss8250 *lpss, struct uart_port *port)
+{
+	return 0;
+}
+
 #ifdef CONFIG_SERIAL_8250_DMA
 static const struct dw_dma_platform_data qrk_serial_dma_pdata = {
 	.nr_channels = 2,
@@ -356,6 +361,7 @@ static const struct lpss8250_board byt_board = {
 static const struct lpss8250_board ehl_board = {
 	.freq = 200000000,
 	.base_baud = 12500000,
+	.setup = ehl_serial_setup,
 };
 
 static const struct lpss8250_board qrk_board = {