pwm: tachometer: return period & duty cycles from tachometer driver

pwm: tachometer: return period & duty cycles from tachometer driver

Return period & duty cycles in nano seconds from tachometer instead of
passing calculated rotations per minute value.

Update pwm sysfs node "rpm" such that it measures the rotations
per minute using period value recevied from pwm tachometer driver.

Change-Id: I1cd2daa1911286e25cecbe50a679d34d86c6f1f1
Signed-off-by: R Raj Kumar <rrajk@nvidia.com>
Reviewed-on: http://git-master/r/1485766
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>
(cherry picked from commit 03bac8937ae15a75f05aa246b6a0a800e49fc16e)