block: declare all partition detection routines in check.h

There is no good reason to include one header per partition type in
core.c.  Instead move the prototypes for the detection routins to
check.h, and remove all now empty headers in block/partitions/.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>