ltp-guf-tests: add support for baud rates above 230400 in serial test (refs #40783)

* Our hardware supports more baud rates than the test did. Add support for baud rates above 230400.

Change-Id: Ic1f0ad2244b84881ef0a8bb952d3ec27825cd569

testcases/serial/serial.c

@@ -88,6 +88,17 @@ static speed_t parse_baud(int baud)
 		case 57600:		return  B57600;
 		case 115200:	return  B115200;
 		case 230400:	return  B230400;
+		case 460800:	return  B460800;
+		case 500000:	return  B500000;
+		case 576000:	return  B576000;
+		case 921600:	return  B921600;
+		case 1000000:	return  B1000000;
+		case 1152000:	return  B1152000;
+		case 1500000:	return  B1500000;
+		case 2000000:	return  B2000000;
+		case 2500000:	return  B2500000;
+		case 3000000:	return  B3000000;
+		case 3500000:	return  B3500000;
 	}
 	return  -1;
 }