pwm: rockchip: Use same PWM ops for each IP

Just use the same PWM ops for each IP, and get rid of the ops in struct
rockchip_pwm_data, but still define the three different instances of the
struct to use common interface for each IP.

Signed-off-by: David Wu <david.wu@rock-chips.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>