Add definitions for 440EPx/GRx SDRAM controller to ppc440.h

Add definitions for 440EPx/GRx SDRAM controller to ppc440.h

This patch adds the Denali SDRAM controller definitions to "ppc440.h".
It also fixes two typos in the definitions, so the board-specific
"sdram.h" files containing these definitions are also fixed to avoid
compiler warnings.

Signed-off-by: Larry Johnson <lrj@acm.org>