virtio_page_per_vq: enhance input event file

[dzhengfy]

Regarding /dev/input/event* files, there might be some different situation. For example,

• No event file exsit at all
• Only /dev/input/event0 exists
• Only /dev/input/event1 exists
• Both /dev/input/event0 and /dev/input/event1 exists
• and more ...

So this patch is intending to support above situations instead of hardcoding with event1.