cros_generate_update_payload: Always copy using 8 MiB buffers.

dd allows to pass an offset and length not alligned with the block size
but still perform the copy using bigger blocks. This patch always uses
8 MiB blocks when extracting the partitions.

BUG=None
TEST=`cros_generate_update_payload --extract` still works and runs
faster when partitions are not 2 MiB alligned.

Change-Id: I087378b487b0c57ab355d6d08cadcc14f2b5da48
Reviewed-on: https://chromium-review.googlesource.com/283562
Trybot-Ready: Alex Deymo <deymo@chromium.org>
Tested-by: Alex Deymo <deymo@chromium.org>
Reviewed-by: Gabe Black <gabeblack@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
1 file changed