Use bitfield in GPS HAL.

Test: compiles
Change-Id: I200a1cecddffb57596b9958564d2bf6be982cbdc
diff --git a/gnss/1.0/IGnssCallback.hal b/gnss/1.0/IGnssCallback.hal
index 041f949..97a28e2 100644
--- a/gnss/1.0/IGnssCallback.hal
+++ b/gnss/1.0/IGnssCallback.hal
@@ -111,7 +111,7 @@
         /*
          * Contains additional data about the given SV.
          */
-        GnssSvFlags svFlag;
+        bitfield<GnssSvFlags> svFlag;
     };
 
     /*