arm: mx6: Remove SPI support from WRU-IV baseboard

This patch removes the SPI support from the WRU-IV baseboard as its
not used at all.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Clemens Gruber <clemens.gruber@pqgruber.com>
Cc: Markus Niebel <Markus.Niebel@tq-group.com>
Cc: Stefano Babic <sbabic@denx.de>
Tested-by: Clemens Gruber <clemens.gruber@pqgruber.com>
Reviewed-by: Jagan Teki <jteki@openedev.com>