Convert nsec to usec in encoder buffer timestamps

Timestamps related to video buffers are in nanoseconds
but lower layers of the system expect this information to
be presented in microseconds. To keep compatibility with remaining
part of the system and do not modify logic related to handling
information about time in ARCVM, timestamps for encoder buffers are
adjusted to hold value in microseconds.

BUG=b:230794145
TEST=android.media.cts.VideoCodecTest#testBasicAVCCBR
Change-Id: I67222bca7dc5e8eb829f519b0235c4320ce37264
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/4062034


Commit-Queue: Bartłomiej Grzesik <bgrzesik@google.com>
Reviewed-by: Marcin Wojtas <mwojtas@google.com>
Tested-by: Patryk Busse <pbu@semihalf.com>
Signed-off-by: Slawomir Rosek <srosek@google.com>