thunderbolt: debugfs: Fix margin debugfs node creation condition

The margin debugfs node controls the "Enable Margin Test" field of the
lane margining operations. This field selects between either low or high
voltage margin values for voltage margin test or left or right timing
margin values for timing margin test.

According to the USB4 specification, whether or not the "Enable Margin
Test" control applies, depends on the values of the "Independent
High/Low Voltage Margin" or "Independent Left/Right Timing Margin"
capability fields for voltage and timing margin tests respectively. The
pre-existing condition enabled the debugfs node also in the case where
both low/high or left/right margins are returned, which is incorrect.
This change only enables the debugfs node in question, if the specific
required capability values are met.

Signed-off-by: Aapo Vienamo <aapo.vienamo@linux.intel.com>
Fixes: d0f1e0c2

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