ioengine: Add libcufile I/O engine

ioengine: Add libcufile I/O engine

The libcufile I/O engine uses NVIDIA GPUDirect Storage (GDS) cuFile API to perform
synchronous I/O directly against GPU buffers via nvidia-fs and a GDS-supported
filesystem.

'configure --enable-libcufile' enables the libcufile engine.

CFLAGS must specify the location of CUDA and cuFile headers.
e.g. CFLAGS="-I/usr/local/cuda/include -I/usr/local/cuda/lib64"

LDFLAGS must specify the location of CUDA and cuFile libraries.
e.g. LDFLAGS="-L/usr/local/cuda/lib64"

The paths used in CFLAGS and LDFLAGS depend upon the build host's
CUDA installation.

libcufile adds the following optons: gpu_dev_ids, cuda_io
Usage is documented in HOWTO, fio.1, examples/libcufile-cufile.fio
and examples/libcufile-posix.fio.

Note that enabling verify when cuda_io=cufile necessitates
cudaMemcpy() to populate the GPU buffer on a write and populate the
CPU buffer on a read. The primary goal of GDS is to not copy data
between CPU and GPU buffers.

Signed-off-by: Brian T. Smith <bsmith@systemfabricworks.com>