block/bdev: lift block size restrictions to 64k

We now can support blocksizes larger than PAGE_SIZE, so in theory
we should be able to lift the restriction up to the max supported page
cache order. However bound ourselves to what we can currently validate
and test. Through blktests and fstest we can validate up to 64k today.

Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20250221223823.1680616-8-mcgrof@kernel.org


Signed-off-by: Christian Brauner <brauner@kernel.org>