x86: use trampoline e820 buffer for BIOS interface only

x86: use trampoline e820 buffer for BIOS interface only

Instead of using the E820 raw buffer for BIOS, EFI and multiboot based
memory map information use it for the BIOS interface only. This will
enable us to support more E820 entries than the limited trampoline
located buffer can.

Add a new raw e820 table for common purpose and copy the BIOS buffer
to it. Doing the copying in assembly avoids the need to export the
symbols for the BIOS E820 buffer and number of entries.

Signed-off-by: Juergen Gross <jgross@suse.com>
[jb: eliminate an unneeded local variable]
Reviewed-by: Jan Beulich <jbeulich@suse.com>