[audio] Remove playback hardening for certain usages

Exempt system usages and VIRTUAL_SOURCE from playback hardening.

Pull some permission related utils into a header for reuse.

Test: atest android.virtualdevice.cts.audio.VirtualAudioTest
Bug: 376481063
Bug: 385445566
Flag: com.android.media.audio.hardening_impl
Change-Id: I0bc5537813240abc6e9fb1b5393f1980c0bd850e