layers: Add some val/state-update todos
layers: Add some val/state-update todos

Couple of routines combine state updates and validation, adding a
note for future work.

Change-Id: I417025bbcabfd3e80ccefe166bc6ea3497222753

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools