gpio: xilinx: Drop architecture dependencies

The driver does not have any real architecture dependencies. To avoid
listing each architecture that might use this driver on some
FPGA-enabled platform, drop these dependencies.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Acked-by: Moritz Fischer <moritz.fischer@ettus.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>