badblocks: Add core badblock management code

badblocks: Add core badblock management code

Orabug: 22913653

Take the core badblocks implementation from md, and make it generally
available. This follows the same style as kernel implementations of
linked lists, rb-trees etc, where you can have a structure that can be
embedded anywhere, and accessor functions to manipulate the data.

The only changes in this copy of the code are ones to generalize
function/variable names from md-specific ones. Also add init and free
functions.

Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
(cherry picked from commit 9e0e252a048b0ba5066f0dc15c3b2468ffe5c422)
Signed-off-by: Dan Duval <dan.duval@oracle.com>