kvm tools: Use ioport context to control blk devices

kvm tools: Use ioport context to control blk devices

Since ioports now has the ability to pass context to its
callbacks, we can implement multiple blk devices more efficiently.

We can get a ptr to the 'current' blk dev on each ioport call, which
means that we don't need to keep track of the blk device allocation
and ioport distribution within the module.

The advantages are easier management of multiple blk devices and
removal of any hardcoded limits to the amount of possible blk
devices.

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