[gps] Conditionally set default GPS port

AeroCore uses ttyS0 not ttyS3 as the serial port connected to the GPS.
Now, a board can set GPS_DEFAULT_UART_PORT to override the default setting
in a board-specific fashion.

Signed-off-by: Ash Charles <ashcharles@gmail.com>

src/drivers/boards/aerocore/board_config.h

@@ -73,6 +73,7 @@ __BEGIN_DECLS
 /* GPS */
 #define GPIO_GPS_NRESET		(GPIO_OUTPUT|GPIO_PUSHPULL|GPIO_OUTPUT_SET|GPIO_PORTC|GPIO_PIN5)
 #define GPIO_GPS_TIMEPULSE	(GPIO_INPUT|GPIO_FLOAT|GPIO_PORTC|GPIO_PIN4)
+#define GPS_DEFAULT_UART_PORT	"/dev/ttyS0"
 
 /* SPI3--Sensors */
 #define PX4_SPI_BUS_SENSORS	3

src/drivers/drv_gps.h

@@ -43,12 +43,12 @@
 #include <stdint.h>
 #include <sys/ioctl.h>
 
+#include "board_config.h"
+
 #include "drv_sensor.h"
 #include "drv_orb_dev.h"
 
-#ifdef CONFIG_ARCH_BOARD_AEROCORE
-#define GPS_DEFAULT_UART_PORT "/dev/ttyS0"
-#else
+#ifndef GPS_DEFAULT_UART_PORT
 #define GPS_DEFAULT_UART_PORT "/dev/ttyS3"
 #endif