NFSv4.1 move deviceid cache to filelayout driver

No need for generic cache with only one user.
Keep a simple hash of deviceids in the filelayout driver.

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Acked-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>