This moves the SPI pin control table out of the board file
and into the device tree. Move the specific setting for
SSP0 on the HREFprev60 into the prev60-specific DTS file.
The SPI2 configuration is not really connected to any device,
as it will conflict with GPIO218 which is used on all HREFs.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>