kvm tools: Implement keyboard reset method

kvm tools: Implement keyboard reset method

Implement the keyboard reset method which allows guest kernel
to reboot the guest using the keyboard controller.

This will allow guest kernel to reboot the guest when it needs to,
for example - kernel panic (when passing "panic=1" as kernel parameter).

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