arm: dts: msm: Add avtimer info for msm8996

avtimer is used for synchronization of audio and video
during the playback/capture usecase. This change adds
avtimer register addresses in device tree for msm8996
target.

Change-Id: Ib027b429258061fa0d4777fbf412bf38c5dbaec0
Signed-off-by: Kuirong Wang <kuirongw@codeaurora.org>