kvm tools: Add optional parameter used in ioport callbacks

kvm tools: Add optional parameter used in ioport callbacks

Allow specifying an optional parameter when registering an
ioport range. The callback functions provided by the registering
module will be called with the same parameter.

This may be used to keep context during callbacks on IO operations.

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