LU-9679 osc: convert oe_refc to kref

LU-9679 osc: convert oe_refc to kref

oe_refc is used like a kref, so make it one.

As cl_object_put() needs an 'env', we cannot quite use
kref_put() as intended.  Maybe that can be fixed one day.

This requires kref_read() to be provided for older kernels.

The original Linux-commit also converted oe_users to a refcount_t
but that was later reverted.

Linux-Commit: 35ea2a7c694b ("lustre: osc: convert oe_refc and oe_users
	to kref and refcount_")

Signed-off-by: Mr NeilBrown <neilb@suse.com>
Change-Id: I42fd17c4261b85b273387936b97fce463273e2b8
Reviewed-on: https://review.whamcloud.com/37601
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>