ARM: CSR: extend the compatibility of gpio controller to pinmux in dts

gpio controller handles the switch of gpio and pinmux. And drivers/pinctrl/pinmux-sirf.c
will contain both gpio and pinmux.

Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Barry Song <Baohua.Song@csr.com>