Arm: arch: configs: Add AVTIMER_CONFIG to msm8994

Add AVTIMER_CONFIG to msm8994. It enables to read avtimer
values. This AVTIMER_CONFIG will enable the avtimer driver so
isp can switch to avtimer timestamps for the buffers when
VideoTelephony(VT) is used.

Change-Id: Id743657c7b98b8fa82985e05d52079d1c769d41a
Signed-off-by: Sreesudhan Ramakrish Ramkumar <srramku@codeaurora.org>