dt-bindings: hwmon: aspeed-pwm-tacho: Add reset node

The device tree bindings are updated to document the resets phandle, and
the example is updated to match what is expected for both the reset and
clock phandle.

Note that the bindings should have always had the reset controller, as
the hardware is unusable without it.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>