vfio/common: Use a single tracepoint for skipped sections

vfio/common: Use a single tracepoint for skipped sections

In preparation to turn more of the memory listener checks into
common functions, one of the affected places is how we trace when
sections are skipped. Right now there is one for each. Change it
into one single tracepoint `vfio_listener_region_skip` which receives
a name which refers to the callback i.e. region_add and region_del.

Suggested-by: Avihai Horon <avihaih@nvidia.com>
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/r/20230307125450.62409-7-joao.m.martins@oracle.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>