[PATCH] hwmon: Sysfs interface documentation update, 1 of 2

This patch cleans up hwmon sysfs documentation file, plus introduces
the description of DC/PWM selection for fan speed control.

Signed-off-by: Rudolf Marek <r.marek@sh.cvut.cz>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>