SPMV using onemkl and SYCL - for discussion purposes

[IgorBaratta]

• Simplified the Matrix class (removed Eigen backend). Added two constructors, one if buffers using buffers (tested with dolfinx.sycl repository) and one with vectors (data is copied from the local host to local device).
• Added distributed Vector Class with some basic operations (dot, norm, update, b=Ax, operator+)
• Added few additional tests

Can be linked to cublas or MKL via oneMKL (just one API).

I'm not sure which matrix and vector cold be used for demos/restrictmain.cpp