ARM: dts: NSP: Add GPIO reboot method to bcm958625hr DTS file

Add the ability to reboot the bcm958625hr board via GPIO.
Unfortunately, not all of the NSP based boards use the same GPIO pin and
one doesn't have the ability to reboot via GPIO at all.  So, this will
need to be specified per DTS file.

Signed-off-by: Jon Mason <jon.mason@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>