pwm: Add power management descriptions

This patch adds power management descriptions that consumers should
implement it.
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

Documentation/pwm.txt

@@ -65,6 +65,10 @@ period). struct pwm_args contains 2 fields (period and polarity) and should
 be used to set the initial PWM config (usually done in the probe function
 of the PWM user). PWM arguments are retrieved with pwm_get_args().
 
+All consumers should really be reconfiguring the PWM upon resume as
+appropriate. This is the only way to ensure that everything is resumed in
+the proper order.
+
 Using PWMs with the sysfs interface
 -----------------------------------
 
@@ -141,6 +145,9 @@ The implementation of ->get_state() (a method used to retrieve initial PWM
 state) is also encouraged for the same reason: letting the PWM user know
 about the current PWM state would allow him to avoid glitches.
 
+Drivers should not implement any power management. In other words,
+consumers should implement it as described in the "Using PWMs" section.
+
 Locking
 -------