msm: vidc: Send timestamp as microsec during ETB

In v4l2 vb2_buffer timestamp is stored in nano secs.
This is converted to micro seconds before ETB to firmware.
Similarly during FBD timestamp in micro seconds is
converted to nano seconds while storing in vb2_buffer.

CRs-Fixed: 2020833
Change-Id: I80947a992a3f96de9acc4dbdc025952c17c9b116
Signed-off-by: Vaibhav Deshu Venkatesh <vdeshuve@codeaurora.org>