pinctrl: sirf: enable the driver support new SiRFmarco SoC

The driver supports old up SiRFprimaII SoCs, this patch makes it support
the new SiRFmarco as well.
SiRFmarco, as a SMP SoC, adds new SIRFSOC_GPIO_PAD_EN_CLR registers, to
disable GPIO pad, we should write 1 to the corresponding bit in the new
CLEAR register instead of writing 0 to SIRFSOC_GPIO_PAD_EN.

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