ocl: pointer-arithmetic for device-pointers #1512

Job	Run time
build-on-cuda (OPENMP=ON)	8m 11s
build-and-test (MPI=ON, OPENMP=ON, SMM=blas, openmpi)	4m 7s
build-on-opencl (OPENMP=ON, SMM=libxsmm)	8m 47s
build-and-test (MPI=ON, OPENMP=ON, SMM=blas, mpich)	4m 10s
build-on-rocm (OPENMP=ON, G2G=ON)	4m 9s
build-and-test (MPI=ON, OPENMP=ON, SMM=libxsmm, openmpi)	4m 2s
build-on-rocm (OPENMP=ON, G2G=OFF)	4m 3s
pre-commit	1m 11s
build-and-test (MPI=ON, OPENMP=ON, SMM=libxsmm, mpich)	3m 45s
build-and-test (MPI=ON, OPENMP=OFF, SMM=blas, openmpi)	9m 4s
build-and-test (MPI=ON, OPENMP=OFF, SMM=blas, mpich)	9m 41s
build-and-test (MPI=ON, OPENMP=OFF, SMM=libxsmm, openmpi)	8m 56s
build-and-test (MPI=ON, OPENMP=OFF, SMM=libxsmm, mpich)	9m 15s
build-and-test (MPI=OFF, OPENMP=ON, SMM=blas, openmpi)	5m 11s
build-and-test (MPI=OFF, OPENMP=ON, SMM=libxsmm, openmpi)	5m 14s
build-and-test (MPI=OFF, OPENMP=OFF, SMM=blas, openmpi)	3m 29s
build-and-test (MPI=OFF, OPENMP=OFF, SMM=libxsmm, openmpi)	3m 30s
Combine & check coverage.	44s
	1h 37m 29s

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