The granular residue accounting code uses certain variables specifically
for residue accounting. Document these in the structure declaration.
Also move around some elements and group them together.

Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NJoel Fernandes <joelf@ti.com>
Signed-off-by: NVinod Koul <vinod.koul@intel.com>