linux-firmware: Add serdes configuration firmware for Keystone 2 devices

Add initial K2 SerDes Firmware binary to the linux-firmware repo.  This
binary is subject to the licensing defined in the LICENCE.ti-keystone
found in the top level directory of this repo. This firmware is required
to support Keystone 2 serdes phy for GBE, PCIe and XGBE modes.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>