x86: Fill in the dram info using the e820 map on coreboot/x86

This way when that dram "banks" are displayed, there's some useful information
there. The number of "banks" we claim to have needs to be adjusted so that it
covers the number of RAM e820 regions we expect to have/care about.

This needs to be done after "RAM" initialization even though we always run
from RAM. The bd pointer in the global data structure doesn't automatically
point to anything, and it isn't set up until "RAM" is available since, I
assume, it would take too much space in the very constrained pre-RAM
environment.

Signed-off-by: Gabe Black <gabeblack@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>