cleanup updating the size of block devices v3

[Christoph Hellwig <hch@lst.de>]

Hi Jens,

this series builds on top of the work that went into the last merge window,
and make sure we have a single coherent interfac for updating the size of a
block device.

Changes since v2:
 - rebased to the set_capacity_revalidate_and_notify in mainline
 - keep the loop_set_size function
 - fix two mixed up acks
 
Changes since v1:
 - minor spelling fixes