ppc4xx: PPC440EPx Emit DDR0 registers on machine check interrupt

This patch prints the DDR status registers upon machine check
interrupt on the 440EPx/GRx. This can be useful especially when
ECC support is enabled.

I added some small changes to the original patch from Niklaus to
make it compile clean.

Signed-off-by: Niklaus Giger <niklaus.giger@nestal.com>
Signed-off-by: Stefan Roese <sr@denx.de>