dt-bindings: phy: Add defines for AM64 SERDES Wrapper

Add defines for AM64 SERDES Wrapper.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Link: https://lore.kernel.org/r/20210721155849.20994-5-kishon@ti.com