avtimer: Update avtimer driver to parse driver tree data

LPASS exposes registers from which timestamp can be
read by clients for audio & video synchronization.
Change adds to retrieve the register address of AV
timer in LPASS passing from driver tree data.

Change-Id: Id7cf3455e22ddc27f5350a7a37c3b40d44eb0873
Signed-off-by: Gopikrishnaiah Anandan <agopik@codeaurora.org>