hw/virtio: Move vhost-user-input into virtio folder

hw/virtio: Move vhost-user-input into virtio folder

vhost-user-input is in the input folder.  On the other hand, the folder
'hw/virtio' maintains other virtio stubs (e.g. I2C, RNG, GPIO, etc).

This patch moves vhost-user-input into the virtio folder for better code
organization.  No functionality change.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Message-Id: <20231120043721.50555-4-leo.yan@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240104210945.1223134-11-alex.bennee@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>