decruft genhd.h v2

Hi Jens,

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

Changes since v1:
 - rebased to the latest block tree

Follow-Ups:
- Re: decruft genhd.h v2
  - From: Jens Axboe
- [PATCH 9/9] block: make the init_part_stats return value more logical
  - From: Christoph Hellwig
- [PATCH 1/9] block: mark block_depr static
  - From: Christoph Hellwig
- [PATCH 8/9] block: move the part_stat* helpers from genhd.h to a new header
  - From: Christoph Hellwig
- [PATCH 7/9] block: move block layer internals out of include/linux/genhd.h
  - From: Christoph Hellwig
- [PATCH 6/9] block: move guard_bio_eod to bio.c
  - From: Christoph Hellwig
- [PATCH 5/9] block: unexport get_gendisk
  - From: Christoph Hellwig
- [PATCH 4/9] block: unexport disk_map_sector_rcu
  - From: Christoph Hellwig
- [PATCH 2/9] block: mark part_in_flight and part_in_flight_rw static
  - From: Christoph Hellwig
- [PATCH 3/9] block: unexport disk_get_part
  - From: Christoph Hellwig