pwm: core: Add option to config PWM duty/period with u64 data length

Currently, PWM core driver provides interfaces for configuring PWM
period and duty length in nanoseconds with an integer data type, so
the max period can be only set to ~2.147 seconds. Add interfaces which
can set PWM period and duty with u64 data type to remove this
limitation.

Change-Id: Ic8722088510d447fc939ab6a5014711aef1b832f
Signed-off-by: Fenglin Wu <fenglinw@codeaurora.org>