pinctrl: abx500: Add device tree support

We use the same way to define pin muxing and pin configuration
than for nomadik. So pickup code from pinctrl_nomadik.c to be
able to implement pin multiplexing and pin configuration using
the device tree. Pin configuration uses generic parsing code.

Signed-off-by: Gabriel Fernandez <gabriel.fernandez@st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>