powerpc/85xx: enable coreint for all the 64bit boards

With the patch 7230c564

 (powerpc: Rework lazy-interrupt handling),
it seems that the coreint works pretty well on the 85xx 64bit kernel.
So use the coreint by default for these boards.

Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>