healthd: move healthd_board_init call to Health::Health() c-tor

The invocation is wrapped so that clients of -impl doesn't
have to call healthd_board_init directly.

Test: health VTS test
Test: charger_test
Bug: 69268160

Change-Id: I61f820b80ce6b03fe51ca05d07ed7e09ca369d2d
3 files changed