dt-bindings: phy: Add PHY_TYPE_XPCS definition

Add definition for Ethernet PCS phy type.

Signed-off-by: Dilip Kota <eswara.kota@linux.intel.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-By: Vinod Koul <vkoul@kernel.org>
Link: https://lore.kernel.org/r/6091f0d2a1046f1e3656d9e33b6cc433d5465eaf.1589868358.git.eswara.kota@linux.intel.com


Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>