LU-17015 build: rework upcall cache

LU-17015 build: rework upcall cache

EX-4333 introduced in upcall_cache.c a dependency on md_object.h for
struct lu_ucred. Rework files to move this dependency to a differnt
file, so that upcall_cache.c can be built in client-only mode.

Fixes: fb0082bba1 ("EX-4333 sec: support supplementary groups from client")
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I4bcc7e07a4f4886c5994d17cbef72ea09eb1be1d
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/52670
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>