mm: backing-dev: make bdi_class a static const structure

Now that the driver core allows for struct class to be in read-only
memory, move the bdi_class structure to be declared at build time placing
it into read-only memory, instead of having to be dynamically allocated at
load time.

Link: https://lkml.kernel.org/r/20230620183314.682822-2-gregkh@linuxfoundation.org


Signed-off-by: Ivan Orlov <ivan.orlov0322@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>