Clarify or update ARM/vendor specific information

[SaschaWillems]

Some samples based on the ARM samples have misleading information, e.g. https://github.com/KhronosGroup/Vulkan-Samples/blob/main/samples/performance/layout_transitions/README.adoc#best-practice-summary

The Do's and Dont's seem to refer to ARM GPUs, but they look like those are general guidelines. This has lead to confusion multiple times, with people thinking the points listed here apply to Vulkan in general.

We probably need to look at all the documentation that is ARM specific and update, remove or clearly mark it as ARM specific.