target-i386: Move topology.h to include/hw/i386

This will allow the PC code to use the header, and lets us eliminate the
QEMU_INCLUDES hack inside tests/Makefile.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
