Remove erroneous or extra spd.h #includers.

Many of the spd.h #includers don't need it,
and wanted to have spd_sdram() declared instead.
Since they didn't get that, some also had open
coded extern declarations of it instead or as well.
Fix it all up by using spd_sdram.h where needed.

Signed-off-by: Jon Loeliger <jdl@freescale.com>