memory protection: implicit kernel object permissions

[zephyrbot]

Reported by Andrew Boie:

As a developer, it would be really nice to have a way to assign object permissions to threads statically, given that the objects and threads are static objects. Would be even nicer to have it be implicit, along the lines of "a static thread has access to any static kernel object declared in the same C source file"

(Imported from Jira ZEP-2585)