CMakeLists.txt: fix misleading logical_target_for_zephyr_elf comment

The comment for:

  set_target_properties(${logical_target_for_zephyr_elf} PROPERTIES
     OUTPUT_NAME ${KERNEL_NAME})

was completely off-topic and making something relatively simple
incredibly puzzling and time-consuming to understand.

Re-order the if(GKSF OR GKOF) clauses so the two initializations of
logical_target_for_zephyr_elf are close to each other and so the very
short clause is not buried at the bottom of the long one.

Other minor logical_target_for_zephyr_elf comment fixes.

Signed-off-by: Marc Herbert <marc.herbert@intel.com>