dt-bindings: phy: Allow defining the SATA AFE TX amplitude

Document a new property which allows the selection of the SATA AFE TX
amplitude in milli Volts. Possible values are 400, 500, 600 and 800mV.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20201022205056.233879-2-f.fainelli@gmail.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>