NFSv4.1: make deviceid cache global

Move deviceid cache from the pnfs files layout driver to the
generic layer in preparation for the objects layout driver.

Signed-off-by: Benny Halevy <bhalevy@panasas.com>

diff --cc fs/nfs/Makefile
Simple merge

diff --cc fs/nfs/nfs4filelayout.c
Simple merge

diff --cc fs/nfs/nfs4filelayout.h
Simple merge

diff --cc fs/nfs/nfs4filelayoutdev.c
Simple merge

diff --cc fs/nfs/pnfs.h
Simple merge

diff --cc fs/nfs/pnfs_dev.c
Simple merge