dt-binding: hwmon: Add NPCM7xx PWM and Fan controller documentation

Added device tree binding documentation for Nuvoton BMC
NPCM7xx Pulse Width Modulation (PWM)  and Fan tach controller.
The Nuvoton BMC NPCM7XX supports 8 PWM controller outputs
and 16 Fan tachometer controller inputs.

Signed-off-by: Tomer Maimon <tmaimon77@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
[groeck: Fixed whitespace errors noticed by git]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>