NVMe: Add compat_ioctl

Make ioctls work for 32-bit applications on 64-bit kernels.  The structures
are defined to be the same for both 32- and 64-bit applications, so
we can use the same handler for both.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>