SPEAr: Remove existing padmux support for SPEAr

We must use pinctrl framework instead of defining per SoC pinmux drivers. This
patch removes existing padmux support present for SPEAr platform.

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