LINUX: add afs_d_alias_lock & _unlock compat wrappers

LINUX: add afs_d_alias_lock & _unlock compat wrappers

Simplify some #ifdefs for HAVE_DCACHE_LOCK by pushing them down into
new helpers in osi_compat.h.

No functional change should be incurred by this commit.

Reviewed-on: https://gerrit.openafs.org/12790
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit 652cd597d9b3cf1a9daccbbf6bf35f1b0cd55a94)

Change-Id: I6aec7d6a21e68011ca10ceaa15e83d80f52fad59
Reviewed-on: https://gerrit.openafs.org/12848
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>