DPC++ CMake configuration

[tcojean]

Gives the ability to select DPC++ hardware parameters from CMake.

This is old code and needs to be retested.

• [x] Fix ELL deadlock on DevEP
• [ ] Fix per_source on CPU through generic file splitting.

Fixes #919

[tcojean]

format!

[ginkgo-bot]

Note: This PR changes the Ginkgo ABI:

Functions changes summary: 21 Removed, 1383 Changed (17196 filtered out), 0 Added functions
Variables changes summary: 0 Removed, 0 Changed, 0 Added variable

For details check the full ABI diff under Artifacts here

[ginkgo-bot]

Error: The following files need to be formatted:

common/unified/matrix/dense_cmnpr.cpp
common/unified/matrix/dense_compute_norm1.cpp
common/unified/matrix/dense_compute_norm2.cpp
common/unified/matrix/dense_css.cpp
common/unified/matrix/dense_kernels_2.cpp
common/unified/matrix/dense_kernels_3.cpp
common/unified/matrix/dense_kernels_4.cpp
common/unified/matrix/dense_kernels_5.cpp
common/unified/matrix/dense_kernels_6.cpp
dpcpp/solver/cb_gmres_kernels.dp.cpp
dpcpp/solver/gmres_kernels.dp.cpp
dpcpp/solver/idr_kernels.dp.cpp

You can find a formatting patch under Artifacts here or run format! if you have write access to Ginkgo