metag: tz1090: instantiate gpio-tz1090-pdc

Instantiate the PDC GPIO controller driver from tz1090.dtsi ready for
when it is merged.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Grant Likely <grant.likely@linaro.org>