dt-bindings: phy: Add RX equalizer properties for Broadcom SATA PHY

Define two new properties: brcm,rx-aeq-mode which allows configuring the
SATA PHY RX equalizers and when "manual" is used, brcm,rx-aeq can be
used to set the exact value.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>