rpma: add librpma_apm_* and librpma_gpspm_* engines

rpma: add librpma_apm_* and librpma_gpspm_* engines

The Remote Persistent Memory Access (RPMA) Library is a C library
created to simplify accessing persistent memory on remote hosts over
Remote Direct Memory Access (RDMA).

The librpma_apm_client and librpma_apm_server is a pair of engines
which allows benchmarking persistent writes achieved via
the Appliance Persistency Method (APM; natively supported by
the librpma library) and regular reads (a part of the RDMA standard).

The librpma_gpspm_client and librpma_gpspm_server is a pair of
engines which allows benchmarking persistent writes achieved via
the General Purpose Persistency Method (GPSPM; build on top of
the librpma API).

The librpma library is available here: https://github.com/pmem/rpma
along with the set of scripts using the newly introduced engines
to construct miscellaneous benchmarking scenarios:
https://github.com/pmem/rpma/tree/master/tools/perf

The full history of the development of the librpma fio engines
is available at: https://github.com/pmem/fio/tree/rpma

Co-Authored-By: Lukasz Dorau <lukasz.dorau@intel.com>
Co-Authored-By: Tomasz Gromadzki <tomasz.gromadzki@intel.com>
Co-Authored-By: Jan Michalski <jan.m.michalski@intel.com>
Co-Authored-By: Oksana Salyk <oksana.salyk@intel.com>