arm: mx6: tqma6: fix build for WRU-IV baseboard

Fix:
 undefined reference to `spi_flash_free'
 undefined reference to `spi_flash_probe'

Signed-off-by: Stefano Babic <sbabic@denx.de>
CC: Stefan Roese <sr@denx.de>
Cc: Markus Niebel <Markus.Niebel@tq-group.com>
Acked-by: Stefan Roese <sr@denx.de>