block: add a bio_add_vmalloc helpers

block: add a bio_add_vmalloc helpers

Add a helper to add a vmalloc region to a bio, abstracting away the
vmalloc addresses from the underlying pages and another one wrapping
it for the simple case where all data fits into a single bio.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20250507120451.4000627-5-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>