Reapply "AudioFlinger: Add Mmap AIDL interface"

Adding "std::" fix for std::atomic_uint32_t in case
stdatomic is not included.

This reverts commit 559379d0.

Prior change did not consider downstream build for
git_main-without-vendor.

Flag: EXEMPT bugfix
Test: validate fail to pass with fix for target komodo-bp3a-userdebug
Bug: 430611780
Bug: 292281786
Bug: 360900435
Change-Id: Ia6662cf331ee778dc5fe2faa38cfc6c6da21371d