Turbostat: introduce 'delta' data sets

This patch replace the 'old = new - old' mecanism with a simpler
'delta = new - old' one
Turbostat: don't hide the actual size of the buffer in some define
Turbostat: move set_temperature_target to setup_all_buffers

setup_all_buffers can be called after a free_all_buffers, which would
remove the tcc_activation_temp