Refactor malloc allocation

[gonzalobg]

Currently, some of the benchmarks allocate memory that's accessed from the kernels using:

• malloc
• aligned_alloc(2MiB, ...)
• C++ new
• vendor specific apis (cudaMallocManaged, etc.)

How the memory is allocated does impact benchmark performance a bit.

I think we should extract these into their own file, to ensure all benchmarks may pick the exact same defaults.