serial: omap: remove warnings about unused functions

They're used by only if CONFIG_PM is enabled, so enclose them
with proper ifdefs. Removes these warnings:

drivers/tty/serial/omap-serial.c:202:12: warning: 'serial_omap_get_context_loss_count' defined but not used [-Wunused-function]
drivers/tty/serial/omap-serial.c:213:13: warning: 'serial_omap_enable_wakeup' defined but not used [-Wunused-function]
Signed-off-by: NGuido Martínez <guido@vanguardiasur.com.ar>
Signed-off-by: NEzequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/omap-serial.c

@@ -199,6 +199,7 @@ static inline void serial_omap_clear_fifos(struct uart_omap_port *up)
 	serial_out(up, UART_FCR, 0);
 }
 
+#ifdef CONFIG_PM
 static int serial_omap_get_context_loss_count(struct uart_omap_port *up)
 {
 	struct omap_uart_port_info *pdata = dev_get_platdata(up->dev);
@@ -219,6 +220,7 @@ static void serial_omap_enable_wakeup(struct uart_omap_port *up, bool enable)
 
 	pdata->enable_wakeup(up->dev, enable);
 }
+#endif /* CONFIG_PM */
 
 /*
  * Calculate the absolute difference between the desired and actual baud