To build using openrng backend follow these steps

.ci/scripts/build.sh --compiler gnu --optimizations sve \
    --target onedal_c --backend-config ref  --plat lnxarm --use-openrng yes
.ci/scripts/build.sh --compiler gnu --optimizations sve \
    --target daal --backend-config ref  --plat lnxarm --use-openrng yes

With this PR, openRNG backend becomes available for builds on
arm machine with ref backend using gnu compiler.
(For the other kinds of ref builds, support can be added in the future)

The script `.ci/env/openrng.sh` builds openrng at `__deps/openrng`.

For more control over the build process, this script can be run before
running the make command. While building using make, the variable
`RNG_BACKEND` should be set to `openrng` for the build to use openRNG backend.

If openRNG is installed in a directory other than `./__deps/openrng`,
the environment variable `OPENRNGROOT` can be set before using the make
command to specify the openRNG build directory.

Signed-off-by: Dhanus M Lal <Dhanus.MLal@fujitsu.com>

Signed-off-by: Dhanus M Lal <Dhanus.MLal@fujitsu.com>

Signed-off-by: Dhanus M Lal <Dhanus.MLal@fujitsu.com>

setting RNG_BACKEND variable based on the backend config in makefile.

Signed-off-by: Dhanus M Lal <Dhanus.MLal@fujitsu.com>