NGRAPH_INTELGPU_ENABLE not available in ngraph version ngraph-bridge tries to use

[tripzero]

ngraph-bridge tries to checkout a commit [1] of ngraph that doesn't seem to support the NGRAPH_INTELGPU_ENABLE option, thus ngraph is compiled without it.

Workaround is to use --ngraph_version="v0.27.0-rc.0" along with --build_intelgpu_backend

NOTE: v0.26.0 appears broken due to cldnn having werror on by default (naughty). 0.27.0-rc.0 appears to have fixed that and it builds.

README should be updated with workaround or build_ngtf.py should be updated to by default use a recent released version of ngraph.

[1] - https://github.com/tensorflow/ngraph-bridge/blob/master/build_ngtf.py#L56