UPSTREAM: pwm: rockchip: Add support for hardware readout

UPSTREAM: pwm: rockchip: Add support for hardware readout

Implement the ->get_state() function to expose initial state.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Tested-by: Brian Norris <briannorris@chromium.org>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
(cherry picked from commit 1ebb74cf3537135f157beddf1a4366070155edda)

Change-Id: Ia7454ce2f96ee814118724fa98bdd41d8b5ae922
Signed-off-by: David Wu <david.wu@rock-chips.com>