input: qapi: define event types

input: qapi: define event types

Define input event types, using qapi.  So we get nicely autogenerated
types for our input events.  And when it comes to qmp support some day
things will be a lot easier.

Types are modeled after the linux input layer.  There are separate
event types for each value.  There is a sync to indicate the end
of a event group.

Mouse events are split into motion events (one for each axis) and
button events, which are grouped by sync.

Keyboard events are using the existing KeyValue type.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>