gpio-exar/8250-exar: Rearrange gpiochip parenthood

Set the parent of the exar gpiochip to its platform device, like other
gpiochips are doing it. In order to keep the relationship discoverable
for ACPI systems, set the platform device companion to the PCI 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>