frdm_kl25z: Remove incorrect references to spi

The kl25z does not have the same spi hardware as the k64f and therefore
cannot use the same spi driver. Remove all references to spi for the
kl25z soc and frdm_kl25z board until we have a valid spi driver.

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>