dt-bindings: power: reset: qnap-poweroff: Drop reference to pm_power_off

Replace reference to pm_power_off (which is an implementation detail)
and replace it with a more generic description of the driver's
functionality.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Acked-by: NMark Rutland <mark.rutland@arm.com>
Acked-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NGuenter Roeck <linux@roeck-us.net>
Signed-off-by: NThierry Reding <treding@nvidia.com>
Signed-off-by: NRob Herring <robh@kernel.org>

Documentation/devicetree/bindings/power/reset/qnap-poweroff.txt

@@ -3,8 +3,7 @@
 QNAP NAS devices have a microcontroller controlling the main power
 supply. This microcontroller is connected to UART1 of the Kirkwood and
 Orion5x SoCs. Sending the character 'A', at 19200 baud, tells the
-microcontroller to turn the power off. This driver adds a handler to
-pm_power_off which is called to turn the power off.
+microcontroller to turn the power off.
 
 Synology NAS devices use a similar scheme, but a different baud rate,
 9600, and a different character, '1'.