health: add health HAL and it's default implementation.

The default Health HAL implementation continues to depend on
libhealthd.<target> BOARD_HAL_STATIC_LIBRARY in order to make
sure healthd continues to work.

New device specific Health HAL implentations don't need to
compile with healthd STATIC_HAL.

Test: Tested healthd with and without the static hal implementation
on Angler.

BUG: b/32724915

Change-Id: I25d439f24a4178666614faf196423ffc8ccafafb
Signed-off-by: Sandeep Patil <sspatil@google.com>