healthd: build 'charger' and 'healthd' binaries

This renames the old '/sbin/healthd' to '/sbin/charger'
which is to be only used in recovery and charger-only mode.

.. and adds a new dynamically linked executable in /system/bin/healthd
to be used as 'healthd' in Android.

   text    data     bss     dec     hex filename
 817404   36704   37960  892068   d9ca4 root/sbin/charger {was healthd}
  72717   11064   12984   96765   179fd system/bin/healthd {*new*}
 890121   47768   50944  988833   f16a1 (TOTALS)

Corresponding changes in recovery and charger-only .rc files are
required change how 'charger' is launched in each mode.

Update the seclable for healthd with the launch path in init.rc

Test: Boot tested and verified all 3 modes (recovery, charge-only,
android)

Change-Id: I4ada27a4c113258c5be1fd10adb0f58232b10024
Signed-off-by: Sandeep Patil <sspatil@google.com>