gpio: dwapb: enable for ARC

Synopsys SDP platform uses DW GPIO controller in design with
ARC cores. So adding ARC to architectures that may select this
GPIO controller.

Even though support for Synopsys SDP is yet to be submitted we'll need
this tiny option enabled at least for properly working interrupts (DW
GPIO controller is used as interrupt controller).

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>