PPC4xx: Use common code for PPC440EPx SDRAM support

 board/amcc/sequoia/sdram.c |  344 +-----------------------------
 board/amcc/sequoia/sdram.h |  505 --------------------------------------------
 board/lwmon5/sdram.c       |  357 ++-----------------------------
 board/lwmon5/sdram.h       |  505 --------------------------------------------
 4 files changed, 26 insertions(+), 1685 deletions(-)

These four patches replace board-specific code for Denali-core SDRAM support with common definitions and functions. Please note:

(1) The changes to "board/amcc/sequoia/sdram.c" break the build for "sequoia_nand".

(2) The changes to "board/lwmon5/sdram.c" seem reasonable, but I have no board on which to test them. If you decide to use them, please test them first. I have modified the functionality so that the data-eye search is now done with with the cache disabled, as in the Denali SPD code.

Best regards,
Larry