Allow untrusted apps to access VrManager.

There is only a single systemapi at the moment that is callable, and it is
protected by a signature/preinstalled permission.

(cherry picked from commit I778864afc9d02f8b2bfcf6b92a9f975ee87c4724)

Bug: 35059826,33297721
Test: manually on a marlin
Change-Id: I3789ce8238f5a52ead8f466dfa3045fbcef1958e