pwm: lpss: Make pwm_lpss_apply() not rely on existing hardware state

pwm: lpss: Make pwm_lpss_apply() not rely on existing hardware state

Before this commit pwm_lpss_apply() was assuming 2 pre-conditions
were met by the existing hardware state:

1. That the base-unit and on-time-div read back from the
control register are those actually in use, so that it
can skip setting the update bit if the read-back value
matches the desired values.

2. That the controller is enabled when the cached
pwm_state.enabled says that the controller is enabled.

As the long history of fixes for subtle (often suspend/resume)
lpss-pwm issues shows, these assumptions are not necessary
always true.

1. Specifically is not true on some (*) Cherry Trail devices
with a nasty GFX0._PS3 method which: a. saves the ctrl reg value.
b. sets the base-unit to 0 and writes the update bit to apply/commit
c. restores the original ctrl value without setting the update bit,
so that the 0 base-unit value is still in use.

2. Assumption 2. currently is true, but only because of the code which
saves/restores the state on suspend/resume. By convention restoring the
PWM state should be done by the PWM consumer and the presence of this
code in the pmw-lpss driver is a bug. Therefor the save/restore code will
be dropped in the next patch in this series, after which this assumption
also is no longer true.

This commit changes the pwm_lpss_apply() to not make any assumptions about
the state the hardware is in. Instead it makes pwm_lpss_apply() always
fully program the PWM controller, making it much less fragile.

*) Seen on the Acer One 10 S1003, Lenovo Ideapad Miix 310 and 320 models
and various Medion models.

Acked-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200903112337.4113-7-hdegoede@redhat.com