apply patch for phases on GPU

Description

First part of a patch to allow for phases on GPU: So far, the use of phases on GPUs was disabled, but the code for it seems to be present. This MR enables the GPUs for lasers, bringing the code to the same level as for CPU runs. However, it turns out that there also are issues with vector fields in non-periodic systems on the CPU, as phases are not initialized correctly. This will have to be addressed in a separate MR.

News snippet

Allow phases on GPU. (part 1)

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.