Following commit cfc4c189 ("pwm: Read initial hardware state at
request time") the Rockchip PWM driver can no longer assume a device's
pwm_state structure has been populated after a call to pwmchip_add().
Consequently, the test in rockchip_pwm_probe() intended to prevent the
driver from stopping PWM devices already enabled by the bootloader no
longer functions reliably and this can lead to the kernel hanging
during startup, particularly on devices like the Pinebook Pro that use
a PWM-controlled backlight for their display.

Avoid this by querying the device directly at probe time to determine
whether or not it is enabled.

Fixes: cfc4c189 ("pwm: Read initial hardware state at request time")
Signed-off-by: Simon South <simon@simonsouth.net>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>