pwm: Improve Kconfig help text

The Kconfig help text should help the user understand what functionality
is provided by an option. This is especially true for new subsystems. An
improved help text is provided by this commit in the hopes of clarifying
the usefulness of the PWM framework.
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Acked-by: Borislav Petkov <bp@alien8.de>

drivers/pwm/Kconfig

 menuconfig PWM
-	bool "PWM Support"
+	bool "Pulse-Width Modulation (PWM) Support"
 	depends on !MACH_JZ4740 && !PUV3_PWM
 	help
-	  This enables PWM support through the generic PWM framework.
-	  You only need to enable this, if you also want to enable
-	  one or more of the PWM drivers below.
-
-	  If unsure, say N.
+	  Generic Pulse-Width Modulation (PWM) support.
+
+	  In Pulse-Width Modulation, a variation of the width of pulses
+	  in a rectangular pulse signal is used as a means to alter the
+	  average power of the signal. Applications include efficient
+	  power delivery and voltage regulation. In computer systems,
+	  PWMs are commonly used to control fans or the brightness of
+	  display backlights.
+
+	  This framework provides a generic interface to PWM devices
+	  within the Linux kernel. On the driver side it provides an API
+	  to register and unregister a PWM chip, an abstraction of a PWM
+	  controller, that supports one or more PWM devices. Client
+	  drivers can request PWM devices and use the generic framework
+	  to configure as well as enable and disable them.
+
+	  This generic framework replaces the legacy PWM framework which
+	  allows only a single driver implementing the required API. Not
+	  all legacy implementations have been ported to the framework
+	  yet. The framework provides an API that is backward compatible
+	  with the legacy framework so that existing client drivers
+	  continue to work as expected.
+
+	  If unsure, say no.
 
 if PWM