block: Kill bio_segments()/bi_vcnt usage

block: Kill bio_segments()/bi_vcnt usage

When we start sharing biovecs, keeping bi_vcnt accurate for splits is
going to be error prone - and unnecessary, if we refactor some code.

So bio_segments() has to go - but most of the existing users just needed
to know if the bio had multiple segments, which is easier - add a
bio_multiple_segments() for them.

(Two of the current uses of bio_segments() are going to go away in a
couple patches, but the current implementation of bio_segments() is
unsafe as soon as we start doing driver conversions for immutable
biovecs - so implement a dumb version for bisectability, it'll go away
in a couple patches)

Signed-off-by: Kent Overstreet <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Neil Brown <[email protected]>
Cc: Nagalakshmi Nandigama <[email protected]>
Cc: Sreekanth Reddy <[email protected]>
Cc: "James E.J. Bottomley" <[email protected]>