libafs: Abstract the Linux lru cache interface
Define static functions afs_lru_cache_init, afs_lru_cache_add and
afs_lru_cache_finalize to handle interfacing with Linux's lru
facilities.
This change's primary purpose is to isolate the preprocessor
conditionals associated with the details of the system lru interfaces to
just these functions and to simplify the areas that utilize lru caching
by removing the preprocessor conditionals.
As Linux's lru facilities change, additional conditional code will be
needed.
Change-Id: I74c94bb712359975e3fd1df85f1b338b215f61b0
Reviewed-on: https://gerrit.openafs.org/14167
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>