Add CPU support for kernels.

Modified `_hamiltonian_cuda.cu` to support CPU as `_hamiltonian_cpu.cpp`.
The changes have been registered in `hamiltonian.py`.

PR: USTC-KnowledgeComputingLab/qmb#34
Co-authored-by: Junkai Xu <[email protected]>
Signed-off-by: Hao Zhang <[email protected]>

Author: hzhangxyz