All Thunderbolt switches (except the root switch) contain a drom which
contains information about the device. Right now we only read the UID.

Add code to read and parse this drom. For now we are only interested in
which ports are disabled and which ports are "dual link ports" (a
physical thunderbolt port/socket contains two such ports).
Signed-off-by: Andreas Noever <andreas.noever@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>