UPSTREAM: thunderbolt: Update documentation with the USB4 information

Update user's and administrator's guide to mention USB4, how it relates
to Thunderbolt and and how it is supported in Linux.

While there add the missing SPDX identifier to the document.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Link: https://lore.kernel.org/r/20191217123345.31850-10-mika.westerberg@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit ea81896dc98f324ff3fb9b1e74b4915a1beb3296)

BUG=b:147460168
TEST=None

Change-Id: I8fed8f49d0463c32e39b3098ce04d82a92ac1639
Signed-off-by: Azhar Shaikh <azhar.shaikh@intel.com>
1 file changed