staging: Disable lustre file system for MIPS, SH, and XTENSA

mips allmodconfig fails with

ERROR: "copy_from_user_page" [drivers/staging/lustre/lustre/libcfs/libcfs.ko]
undefined!

which is due to LUSTRE using copy_from_user_page which is not exported by any
architecture. Unfortunately, LUSTRE can only be built as module, so there is no
easy fix.

MIPS, SH, and optionally XTENSA implement copy_from_user_page as unexported
functions. Disable LUSTRE for those.

Cc: Peng Tao <bergwolf@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>