Replace env_init_counter with something like event group

[Hadatko]

Hi @MichalPrincNXP, from what i see in code i would say that env_init_counter<0 is dead code and rest of code can be rewrtiten to bool logic. Recently i got a knowledge that for global bool knowledge should be used something like https://www.freertos.org/event-groups-API.html.

I may create PR with suggested code if you agree with me.
I am talking about rpmsg_env_freertos.c file.

[MichalPrincNXP]

Sorry, I do not see the weakpoint, I guess using event group would consume a little more RAM. Anyway, your suggestions are welcome.

[Hadatko]

We were informed that good practice is to replace global bool variables with mutexes. Groups consumes less resources than mutexes.