[media] exynos-gsc: propagate timestamps from src to dst buffers

Make gsc-m2m propagate the timestamp field from source to destination
buffers.

Signed-off-by: John Sheu <sheu@google.com>
Signed-off-by: Shaik Ameer Basha <shaik.ameer@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>