kvm tools: Move hardware drivers to hw directory

This patch moves hypervisor native hardware emulation drivers to "hw" directory
like we've done for virtio and disk image code.

Acked-by: Cyrill Gorcunov <gorcunov@gmail.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Pekka Enberg <penberg@kernel.org>