thunderbolt: Add 'boot' attribute for devices

In various cases, Thunderbolt device can be connected by ICM on boot
without waiting for approval from user. Most cases are related to
OEM-specific BIOS configurations. This information is interesting for
user-space as if the device isn't in SW ACL, it may create a friction in
the user experience where the device is automatically authorized if it's
connected on boot but requires an explicit user action if connected
after OS is up. User-space can use this information to suggest adding
the device to SW ACL for auto-authorization on later connections.

Signed-off-by: Yehezkel Bernat <yehezkel.bernat@intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>