kvm tools: Cleanup e820 code

kvm tools: Cleanup e820 code

Several cleanups in the patch:
 - Use kernel headers for e820 types and definitions.
 - A byte sized entry count for e820 enteries was used,
this should be dword sized. Update in-memory layout and
bios code to fix it.
 - Use struct e820map to calculate offsets used by bios code.

Reviewed-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>