led: qti-tri-led: Use u64 to support longer on/off duration

Use u64 data type for PWM period/duty setting so that the PWM
interfaces can accept bigger values to set longer on/off blinking
duration.

Change-Id: I9b0d4af431336f8dd4098057f1af91c45486c2cf
Signed-off-by: Fenglin Wu <fenglinw@codeaurora.org>