mdadm: use kernel raid headers

mdadm: use kernel raid headers

For a years we redefined these headers in mdadm. We should reuse headers
exported by kernel to integrate driver and mdadm better.
Include them and remove mdadm owned headers.

There are 3 defines not available in kernel headers, so define them
directly but put them in ifndef guard to make them transparent later.

Use MD_FEATURE_CLUSTERED instead of MD_FEATURE_BITMAP_VERSIONED. The
value is same, kernel define has different name.

Signed-off-by: Mariusz Tkaczyk <mtkaczyk@kernel.org>