phy: brcm-sata: Allow RX equalizer tuning

Parse the DT properties brcm,rxaeq-mode and brcm,rxaeq-value to
correctly configure the RX equalizer of the PHY. This may be required to
resolve specific signal integrity issues.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>