ntfs: validate and reserve bad clusters at mount

The cluster allocator only consults $Bitmap and never loads
$BadClus:$Bad. A free bitmap bit for a known bad cluster can therefore
place that cluster in the free-space cache and make it available for
new file allocations.

Load the named nonresident $Bad stream and map every attribute extent
before validating full-volume coverage and identity mappings for bad
runs. Reserve only free bits in $Bitmap on writable mounts and flush
the corrections before the initial free-space scan. Keep bad-cluster
counts diagnostic so reservations are accounted for exactly once.

Force read-only mounts with repair advice when $Bad cannot be loaded
or validated, and prevent read-write remounts after such errors. Leave
the bitmap unchanged on read-only mounts and fail mounts on memory
allocation failure. Suppress errors=panic while loading $BadClus so
damaged metadata can fall back to read-only.

Reviewed-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

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