thunderbolt: Add only on-board retimers when !CONFIG_USB4_DEBUGFS_MARGINING

Normally there is no need to enumerate retimers on the other side of the
cable. This is only needed in special cases where user wants to run
receiver lane margining against the downstream facing port of a retimer.
Furthermore this might confuse the userspace tools such as fwupd because
it cannot read the information it expects from these retimers.

Fix this by changing the retimer enumeration code to add only on-board
retimers when CONFIG_USB4_DEBUGFS_MARGINING is not enabled.

Reported-by: AceLan Kao <acelan.kao@canonical.com>
Tested-by: AceLan Kao <acelan.kao@canonical.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219420


Cc: stable@vger.kernel.org
Fixes: ff6ab055 ("thunderbolt: Add receiver lane margining support for retimers")
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>