FS-Cache: Count the number of initialised operations

Count and display through /proc/fs/fscache/stats the number of initialised
operations.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Steve Dickson <steved@redhat.com>
Acked-by: Jeff Layton <jeff.layton@primarydata.com>

diff --cc Documentation/filesystems/caching/fscache.txt
Simple merge

diff --cc fs/fscache/internal.h
Simple merge

diff --cc fs/fscache/operation.c
Simple merge

diff --cc fs/fscache/stats.c
Simple merge