common/atomicwrites: add helper for multi block atomic writes

common/atomicwrites: add helper for multi block atomic writes

Add a helper to check that we can perform multi block atomic writes. We will
use this in the following patches that add testing for large atomic writes.
This helper will prevent these tests from running on kernels that only support
single block atomic writes.

Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>