pinctrl: Add SPEAr pinctrl drivers

This adds pinctrl driver for SPEAr platform. It also updates MAINTAINERS file
for SPEAr pinctrl drivers.

Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Stephen Warren <swarren@wwwdotorg.org>