This adds support for single-step. There isn't much to do on the QEMU
side as after we set-up the request for single step via the debug ioctl
it is all handled within the kernel.

The actual setting of the KVM_GUESTDBG_SINGLESTEP flag is already in the
common code. If the kernel doesn't support guest debug the ioctl will
simply error.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 1449599553-24713-4-git-send-email-alex.bennee@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>