Rename the global mic disable setting

The current implementation of the user microphone disable privacy
setting has led to some confusion and readability issues. Originally
meant to denote meaning along the lines of 'the user's microphone
disable switch is enabled', the logic (and reviews) have turned out
slightly cumbersome. Refactoring it to simply mean 'microphone
access', would be easier to implement, review and maintain. This CL
renames the enum, the reworked logic will be in an accompanying CL.

Bug: 183416485
Test: atest VtsHalContexthubV1_2TargetTest
Change-Id: I85c95f4a6ee5cb0db7547c318d30b72f740e6d9b