ocl: pointer-arithmetic for device-pointers #1494

Job	Run time
build-on-cuda (OPENMP=ON)	8m 30s
build-and-test (MPI=ON, OPENMP=ON, SMM=blas, openmpi)	4m 22s
pre-commit	1m 6s
build-on-rocm (OPENMP=ON, G2G=ON)	4m 0s
build-on-rocm (OPENMP=ON, G2G=OFF)	3m 58s
build-and-test (MPI=ON, OPENMP=ON, SMM=blas, mpich)	4m 14s
build-and-test (MPI=ON, OPENMP=ON, SMM=libxsmm, openmpi)	3m 59s
build-and-test (MPI=ON, OPENMP=ON, SMM=libxsmm, mpich)	3m 52s
build-on-opencl (OPENMP=ON, SMM=libxsmm)	8m 31s
build-and-test (MPI=ON, OPENMP=OFF, SMM=blas, openmpi)	9m 51s
build-and-test (MPI=ON, OPENMP=OFF, SMM=blas, mpich)	9m 31s
build-and-test (MPI=ON, OPENMP=OFF, SMM=libxsmm, openmpi)	9m 32s
build-and-test (MPI=ON, OPENMP=OFF, SMM=libxsmm, mpich)	9m 44s
build-and-test (MPI=OFF, OPENMP=ON, SMM=blas, openmpi)	5m 15s
build-and-test (MPI=OFF, OPENMP=ON, SMM=libxsmm, openmpi)	5m 28s
build-and-test (MPI=OFF, OPENMP=OFF, SMM=blas, openmpi)	3m 31s
build-and-test (MPI=OFF, OPENMP=OFF, SMM=libxsmm, openmpi)	3m 29s
Combine & check coverage.	1m 23s
	1h 40m 16s

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