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

Documentation/devicetree/bindings/phy/brcm-sata-phy.txt

@@ -38,6 +38,9 @@ Sub-nodes optional properties:
 - brcm,rxaeq-value: when 'rxaeq-mode' is set to "manual", provides the RX
   equalizer value that should be used. Allowed range is 0..63.
 
+- brcm,tx-amplitude-millivolt: transmit amplitude voltage in millivolt.
+  Possible values are 400, 500, 600 or 800 mV.
+
 Example
 	sata-phy@f0458100 {
 		compatible = "brcm,bcm7445-sata-phy", "brcm,phy-sata3";