Move native_init() from ctor to handler

Moves potentially slow reponses to native_init() for
GNSS HAL off the main system service startup
thread to the LocationManagerService handler

Bug: 38362097
Bug: 63707763
Test: GNSS still works on device, boot logcat as expected
Change-Id: If3e6735fdcf2b41cb743878154e8c03fa27f725b