Extend test suite to validate zero copy API.
Add stress tests.
Add support for cache in the test. Test is not emulating cache
but ensures that buffer works correctly with cache enabled.
Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>
Move icmsg_buf to lib/os and rename to spsc_pbuf (Single Producer
Single Consumer Packet Buffer). It is a generic module and initially
was created as internal module for ipc service.
Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>
