USB: serial: sierra: clean up special-interface handling

Clean up the handling of special interfaces that either should be
ignored or that need a larger number of URBs.

Commit 66f092ed

 ("USB: serial: sierra: unify quirk handling logic")
replaced the previous is_blacklisted() and is_highmemory() helpers with
a single is_quirk() helper which made it even harder to understand what
the interface lists were used for.

Rename the interface-list struct, its members and the interface-lookup
helper and restructure the code somewhat in order to make it more
self-explanatory.

Link: https://lore.kernel.org/r/20200713153936.18032-1-johan@kernel.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>