pinctrl: add a group-specific hog macro

To create elegant tables for pinmux hogs on the PXA MMP platform,
we need this hog macro that can specify both function and group in
one go.

Acked-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Haojian Zhuang <haojian.zhuang@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>