gnss: add mtk receiver type support

Add an MTK (Mediatek) type to the "GNSS_TYPE" attribute.

Note that MTK receivers support a subset of NMEA 0183 with vendor
extensions.

Signed-off-by: Loys Ollivier <lollivier@baylibre.com>
Signed-off-by: Johan Hovold <johan@kernel.org>

include/linux/gnss.h

@@ -22,6 +22,7 @@ enum gnss_type {
 	GNSS_TYPE_NMEA = 0,
 	GNSS_TYPE_SIRF,
 	GNSS_TYPE_UBX,
+	GNSS_TYPE_MTK,
 
 	GNSS_TYPE_COUNT
 };