gnss: update supported baud rates

The Septentrio GNSS driver requires certain baud rates to test all the
supported baud rates of the receiver. Without these changes, certain
"non-standard" ones would print an error to the MAVLink console when the
driver was started through the console.

platforms/nuttx/src/px4/common/SerialImpl.cpp

@@ -97,12 +97,20 @@ bool SerialImpl::configure()
 
 	case 460800: speed = B460800; break;
 
+	case 500000: speed = B500000; break;
+
+	case 576000: speed = B576000; break;
+
 #ifndef B921600
 #define B921600 921600
 #endif
 
 	case 921600: speed = B921600; break;
 
+	case 1000000: speed = B1000000; break;
+
+	case 1500000: speed = B1500000; break;
+
 	default:
 		speed = _baudrate;
 		PX4_WARN("Using non-standard baudrate: %lu", _baudrate);

platforms/posix/src/px4/common/SerialImpl.cpp

@@ -90,12 +90,20 @@ bool SerialImpl::configure()
 
 	case 460800: speed = B460800; break;
 
+	case 500000: speed = B500000; break;
+
+	case 576000: speed = B576000; break;
+
 #ifndef B921600
 #define B921600 921600
 #endif
 
 	case 921600: speed = B921600; break;
 
+	case 1000000: speed = B1000000; break;
+
+	case 1500000: speed = B1500000; break;
+
 	default:
 		speed = _baudrate;
 		PX4_WARN("Using non-standard baudrate: %u", _baudrate);