Prepare the BIOS data areas before device init.

Prepare the BIOS data areas before device init.

Since we do not run option roms in normal mode nothing was
initializing the BDA/EBDA and yet Linux depends very much
on it having sane values here.  For the most part the kernel
tries to work around this not being initialized, but every
once in awhile (1/300 boots or so) it would end up reading
something that looked sane from BDA but was not and then
it would panic.

In this change the EBDA is unconditionally setup before devices
are initialized.  I'm not set on the location in dev_initialize()
but there does not seem to be another place to hook it in so
that it runs just once for ALL platforms regardless of whether
they use option roms or not. (possibly hardwaremain?)

The EBDA setup code has been moved into its own location in
arch/x86/lib/ebda.c so it can be compiled in even if the option
rom code is not.

The low memory size is still set to 1MB which is enough to make
linux happy without having to hook into each mainboard to get a
more appropriate value.  The setup_ebda() function takes inputs
so it could be changed for a mainboard if needed.

OLD/BROKEN would read garbage.  Examples from different boots:
ebda_addr=0x75e80 lowmem=0x1553400
ebda_addr=0x5e080 lowmem=0x3e51400
ebda_addr=0x7aa80 lowmem=0x2f8a800

NEW/FIXED now reads consistent values:
ebda_addr=0xf6000 lowmem=0x100000

Change-Id: I6cb79f0e3e43cc65f7e5fe98b6cad1a557ccd949
Signed-off-by: Duncan Laurie <dlaurie@google.com>
Reviewed-on: http://review.coreboot.org/769
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>