bsg: make bsg_class a static const structure

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

Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: linux-scsi@vger.kernel.org
Cc: linux-block@vger.kernel.org
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ivan Orlov <ivan.orlov0322@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20230620180129.645646-8-gregkh@linuxfoundation.org


Signed-off-by: Jens Axboe <axboe@kernel.dk>