mpc83xx: Correct the struct spi8xxx in mpc8xxx_spi.h

The commit 04a9e118
cause the 83xx immap broken, so the DMA and PCI will
be failed.

The patch fix the struct spi8xxx and rm struct spi83xx.

Signed-off-by: Dave Liu <daveliu@freescale.com>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>