input: sensors: power down akm8963 during suspend

Vote off regulators during suspend and set sensor gpio to sleep
state for power saving.

CRs-fixed: 669309
Change-Id: I053b20c67b1d5f07f495f800e94b12df1c669faa
Signed-off-by: Bingzhe Cai <bingzhec@codeaurora.org>