gpio-exar/8250-exar: Do not even instantiate a GPIO device for Commtech cards

Commtech adapters need the MPIOs for internal purposes, and the
gpio-exar driver already refused to pick them up. But there is actually
no point in even creating the underlying platform device.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>