Support splitted PSS components (anon, file, and shmem)

[ShirleyFei]

According to [1], Linux kernel has reported separate components (anon, file, and shmem) for PSS in smaps_rollup. This helps understand and tune the memory manager behavior in consumer devices.

Thus collect and show these three indicators for per process:

• Pss_Anon
• Pss_File
• Pss_Shmem

[1]http://lkml.kernel.org/r/20190626234333.44608-1-semenzato@chromium.org

[natoscott]

@ShirleyFei in more recent kernels there's also a new Pss_Dirty row in smaps_rollup, might be a useful addition here.