pata_mpc52xx: driver needs BMDMA

Found by this build-error if BMDMA is disabled:

drivers/ata/pata_mpc52xx.c: In function 'mpc52xx_ata_init_one':
drivers/ata/pata_mpc52xx.c:662: error: 'ata_bmdma_interrupt' undeclared (first use in this function)
...

Move the Kconfig entry to the proper location as needed since
9a7780c9 (libata-sff: make BMDMA optional)

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>