ARM: ux500: move AB8500 DMIC settings to DT

This move the AB8500 DMIC (microphone) pin setup from the board
file to the device tree.

Cc: Patrice Chotard <patrice.chotard@st.com>
Cc: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>