spi/mpc52xx-psc-spi: move probe/remove to proper sections

Probe/remove should be in __devinit/__devexit. Found by a section-mismatch
warning. Also, copy do_remove() over to remove().

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>