zeus-common: some cleanup

* Removed useless TARGET_KERNEL_CUSTOM_TOOLCHAIN definition
* Added & fixed some comments to the source files

Signed-off-by: Michael Bestas <mikeioannina@gmail.com>

Change-Id: I3aa9325b968f28209186fb8e26ee1b2028a29089
Signed-off-by: garwedgess <garethwilliams21@gmail.com>