ventana: make CAN_STBY handling to modle specific

CAN_STBY is a gpio used to put the CAN bus transceiver in a low-power
standby mode.  The GPIO is routed differently depending on the baseboard.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
ventana: add WDIS# gpio for GW52xx

The GW52xx routes a GPIO to the WDIS# pin on miniPCIe socket (pin 20).
Export it and default it to output high (de-asserted).

Signed-off-by: Tim Harvey <tharvey@gateworks.com>