fix: block: add a disk_uevent helper (v5.12)

See upstream commit:

  commit bc359d03c7ec1bf3b86d03bafaf6bbb21e6414fd
  Author: Christoph Hellwig <hch@lst.de>
  Date:   Sun Jan 24 11:02:39 2021 +0100

    block: add a disk_uevent helper

    Add a helper to call kobject_uevent for the disk and all partitions, and
    unexport the disk_part_iter_* helpers that are now only used in the core
    block code.

Change-Id: If6e8797049642ab382d5699660ee1dd734e92c90
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>