Some devices, even non convertible ones, can send incorrect
SW_TABLET_MODE reports.

Add an allow list and accept such reports only from devices in it.

Bug reported for Dell XPS 17 9710 on:
https://gitlab.freedesktop.org/libinput/libinput/-/issues/662Reported-by: Tobias Gurtzick <magic@wizardtales.com>
Suggested-by: Hans de Goede <hdegoede@redhat.com>
Tested-by: Tobias Gurtzick <magic@wizardtales.com>
Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Link: https://lore.kernel.org/r/20210920160312.9787-1-jose.exposito89@gmail.com
[hdegoede@redhat.com: Check dmi_switches_auto_add_allow_list only once]
Signed-off-by: Hans de Goede <hdegoede@redhat.com>