staging/lustre: disable virtual block device for 64K pages

The lustre virtual block device cannot handle 64K pages and fails at compile
time. To avoid running into this error, let's disable the Kconfig option
for this driver in cases it doesn't support.

Reported-by: Dann Frazier <dann.frazier@canonical.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>