pseries: Remove hcalls callback

pseries: Remove hcalls callback

For forgotten historical reasons, PAPR hypercalls for specific virtual IO
devices (oh which there are quite a number) are registered via a callback
in the VIOsPAPRDeviceInfo structure.

This is kind of ugly, so this patch instead registers hypercalls from
device_init() functions for each device type.  This works just as well,
and is cleaner.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>