Merge NX gzip support into next

Merge NX gzip support into next

As described by Haren:

Power9 processor supports Virtual Accelerator Switchboard (VAS) which
allows kernel and userspace to send compression requests to Nest
Accelerator (NX) directly. The NX unit comprises of 2 842 compression
engines and 1 GZIP engine. Linux kernel already has 842 compression
support on kernel. This patch series adds GZIP compression support
from user space. The GZIP Compression engine implements the ZLIB and
GZIP compression algorithms. No plans of adding NX-GZIP compression
support in kernel right now.

Applications can send requests to NX directly with COPY/PASTE
instructions. But kernel has to establish channel / window on NX-GZIP
device for the userspace. So userspace access to the GZIP engine is
provided through /dev/crypto/nx-gzip device with several operations.

An application must open the this device to obtain a file
descriptor (fd). Using the fd, application should issue the
VAS_TX_WIN_OPEN ioctl to establish a connection to the engine. Once
window is opened, should use mmap() system call to map the hardware
address of engine's request queue into the application's virtual
address space. Then user space forms the request as co-processor
Request Block (CRB) and paste this CRB on the mapped HW address using
COPY/PASTE instructions. Application can poll on status flags (part of
CRB) with timeout for request completion.

For VAS_TX_WIN_OPEN ioctl, if user space passes vas_id = -1 (struct
vas_tx_win_open_attr), kernel determines the VAS instance on the
corresponding chip based on the CPU on which the process is executing.
Otherwise, the specified VAS instance is used if application passes
the proper VAS instance (vas_id listed in
/proc/device-tree/vas@*/ibm,vas_id).

Process can open multiple windows with different FDs or can send
several requests to NX on the same window at the same time.