os.linux: Document Attribute Tree for StateProviders

os.linux: Document Attribute Tree for StateProviders

Add documentation to headers for
KernelContextSwitch
KernelCpuUsage
KernelMemory
ActiveTid
InputOutput
Kernel

Change-Id: If95fc67f0a6b765267b4247328e3618b6c000315
Signed-off-by: Loïc Prieur-Drevon <loic.prieurdrevon@gmail.com>
Reviewed-on: https://git.eclipse.org/r/81200
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-by: Hudson CI
Reviewed-by: Genevieve Bastien <gbastien+lttng@versatic.net>
Tested-by: Genevieve Bastien <gbastien+lttng@versatic.net>