ARM: ux500: cut chip-select GPIOs from SSP device

What GPIO pin is used with which device on the SSP/SPI bus
is as board-specific as it gets, so it does not belong here
in the core SoC file, and it is disabled so it doesn't hurt
to delete this.

Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>