decruft genhd.h

Hi Jens,

this series tries to move as much out of genhd.h that doesn't really
belong there.

Follow-Ups:
- Re: decruft genhd.h
  - From: Jens Axboe
- [PATCH 2/8] block: mark part_in_flight and part_in_flight_rw static
  - From: Christoph Hellwig
- [PATCH 8/8] block: move the part_stat* helpers from genhd.h to a new header
  - From: Christoph Hellwig
- [PATCH 7/8] block: move block layer internals out of include/linux/genhd.h
  - From: Christoph Hellwig
- [PATCH 6/8] block: move guard_bio_eod to bio.c
  - From: Christoph Hellwig
- [PATCH 5/8] block: unexport get_gendisk
  - From: Christoph Hellwig
- [PATCH 3/8] block: unexport disk_get_part
  - From: Christoph Hellwig
- [PATCH 4/8] block: unexport disk_map_sector_rcu
  - From: Christoph Hellwig
- [PATCH 1/8] block: mark block_depr static
  - From: Christoph Hellwig