gpio: Remove sta2x11 GPIO driver

The Connext chip has 4 gpio cells looking very similar to those of the
Nomadik, whose gpio/pinctrl driver (already featuring devicetree support)
will be used instead of the sta2x11 specific one.

Signed-off-by: Davide Ciminaghi <ciminaghi@gnudd.com>
Acked-by: Giancarlo Asnaghi <giancarlo.asnaghi@st.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>