ARM: ux500: move SKE pin config to device tree

This moves the SKE keypad pin control table out of the board
file and into the device tree. This was previously set to be
active on all MOP500 and HREF boards but after reading the
schematic this seems incorrect: the HREFv60 and later uses
one of these for MC5 and no reference designs have the SKE
connected to any hardware so just leave the pins alone
in the power-on state.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>