Add 440EPx DDR2 SPD DIMM support

Add 440EPx DDR2 SPD DIMM support

This patch adds SPD DDR2 support for the 440EPx ("Denali") SDRAM
controller.  It should also work on the 440GRx.  It is based on the DDR2
SPD code for the 440EP/440EPx, but makes no provision for DDR1 support.

This code has been tested on prototype Korat boards with three Kingston
DIMMS: 512 MiB ECC (one rank), 512 MiB non-ECC (one rank) and 1 GiB ECC
(two ranks).  The Korat board has a single DIMM socket, but support has
been provided (though not tested) for boards with two DIMM sockets.

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