ext4: FLEX_BG Kernel support v2.

This feature relaxes check restrictions on where each block groups meta
data is located within the storage media.  This allows for the allocation
of bitmaps or inode tables outside the block group boundaries in cases
where bad blocks forces us to look for new blocks which the owning block
group can not satisfy.  This will also allow for new meta-data allocation
schemes to improve performance and scalability.

Signed-off-by: Jose R. Santos <jrs@us.ibm.com>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>