block: share more code for bio addition helpers

block: share more code for bio addition helpers

__bio_iov_iter_get_pages currently open codes adding pages to the bio,
which duplicates a lot of code from bio_add_page and
bio_add_zone_append_page.  Add bio_add_page_int and
bio_add_zone_append_page_int helpers that pass down the same_page
output argument so that __bio_iov_iter_get_pages can reuse the main
add bio to page helpers.

Note that I'd normally call these helpers __bio_add_page and
__bio_add_zone_append_page, but the former is already taken for an
exported API.

Signed-off-by: Christoph Hellwig <hch@lst.de>