udf: support files larger than 1G

Make UDF work correctly for files larger than 1GB.  As no extent can be
longer than (1<<30)-blocksize bytes, we have to create several extents if a
big hole is being created.  As a side-effect, we now don't discard
preallocated blocks when creating a hole.

Signed-off-by: Jan Kara <jack@suse.cz>
Acked-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>