isl923x: Change charger_post_init().
isl923x: Change charger_post_init().

The ISL9237/8 can both be powered by VSYS or AC, therefore, it's not
needed to reinitialize the charger after AC is present.

This commit moves the contents of charger_post_init() into a new init
function that will be run once at HOOK_INIT time.

BUG=b:67964166
BRANCH=None
TEST=make -j buildall

Change-Id: I637b1209f86f686013fee0783914fa1596076fa6
Signed-off-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@google.com>
Reviewed-on: https://chromium-review.googlesource.com/759692
Commit-Ready: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>
Tested-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>
Reviewed-by: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec