Modify malloc common function pointers.

Instead of every function being its own atomic, have a single
pointer that can be used to flip all pointers at once. This avoid cases
where the set of pointers can be in an partial switched state.

Also fix a few inconsistent naming of functions in the file.

Test: Ran unit tests (malloc debug, malloc hooks, perfetto).
Change-Id: I3f66da395414586a3fa87874d80dcdf5f702ed39