m68knommu: update MAX_M68K_DMA_CHANNELS for some plattforms

include/asm-m68knommu/mcfdma.h defines base0-3 for M523x,
M527x and M528x so it looks this has been forgotten.

Signed-off-by: Sebastian Siewior <bigeasy@linutronix.de>
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>