Change calbec interfaces (and related things)

Major changes:

• calbec on GPU is now in OpenACC, CUDA Fortran has been removed, and it is more compatible with ongoing OMP5 developments;
• offload_type variable, set at compile time, is used to distinguish among CPU, CUF/OpenACC and OpenMP5 executions;
• becp_d, bec_type_d removed;
• all using_becp removed;
• modules becmod_gpu and becmod_subs_gpu removed;
• s_psi_gpu removed and substituted with s_psi_acc in OpenACC that uses becp instead of becp_d;
• arrays of derived types (e.g. becpt, alphap, alphapt, becp1 in PHonon) are now allocated only on host, and a temporary scalar bectmp is used on device;
• OS-CDFT on GPU will be temporary broken and will be fixed soon with another MR (see !2167 (merged)).