block: lift blocksize property limit to 2 MiB

block: lift blocksize property limit to 2 MiB

Logical and physical block sizes in QEMU are limited to 32 KiB.

This appears unnecessarily tight, and we've seen bigger block sizes
handy at times.

Lift the limitation up to 2 MiB which appears to be good enough for
everybody, and matches the qcow2 cluster size limit.

Signed-off-by: Roman Kagan <rvkagan@yandex-team.ru>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200528225516.1676602-9-rvkagan@yandex-team.ru>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>