Add name "default" as default to register service

the getService() and registerAsService() methods of interface objects
now have default parameters of "default" for the service name. HALs
will not have to use any service name unless they want to register
more than one service.

Test: make hidl_test; adb sync; adb shell;
data/native_test64/hidl_test64
Run VTS test from go/vtsrun on Sensors, Vr, Nfc
Verify NFC HAL works (turn NFC on and off in Settings)

In support of b/33844934

Change-Id: Ibcc140c3ce7930bff61cda2213c4c9ed4491a964