pinctrl: SPEAr: Create macro for declaring GPIO PINS

Same GPIO pins declarations would be required for other SoCs and that will be a
lot of lines of code. Its better to create common macros for it.

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