icm20602: fix attribute show and add ldo control

In driver icm20602 there is no attribute show on the sysfs and
we need use ldo  to supply the vdd.

Change-Id: Iae1d75da08c4a9b0d905ee06c54d81629851ddfb
Signed-off-by: zhaochen <zhaochen@codeaurora.org>