powerpc/5200: convert mpc52xx_psc_spi to use cs_control callback

mpc52xx_psc_spi driver is the last user of the legacy activate_cs
and deactivate_cs callbacks, so convert the driver to the cs_control
hook and remove the legacy callbacks from fsl_spi_platform_data
struct.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>