This PWM driver can be used to support pwm functions
for on all Rockchip Socs.

The previous chips than RK3288 did not support polarity,
and register layout was different from the RK3288 PWM.

The RK3288 keep the current functions.

RK3328 and the chips after it, which can support hardware lock,
configure duty, period and polarity at next same period, to
prevent the intermediate temporary state.

Signed-off-by: David Wu <david.wu@rock-chips.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>