wayland-info: Add a cmdline option for interface

Currently, wayland-info will query the wl_display and print information
about all the interfaces available.

In some cases however, information about just one specific interface is
required.

This adds a command line option --interface (or -i for short) which
prints the information only for the given interface.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Jonas Ådahl <jadahl@gmail.com>
Closes: #7