msm: dt-binding: add snapshot of audio external clockfor Lahaina

This is a snapshot of the external clock header file as of
msm-4.19 commit <Ib9cca> (add audio external clock header
file for Kona).

Change-Id: Ib9ccac4d28bb21e197cd3ea1563dce2601a0699e
Signed-off-by: Meng Wang <mengw@codeaurora.org>