cutils: trace: use ANDROID_SMP to switch atomics

With inline atomics, trace functions have no non-inline function calls
in the fast (tracing off) path.  To enable this, ANDROID_SMP must be
defined for the project.  Otherwise, normal (non-inline) atomics are
used.

Change-Id: Id1f75bdf7db2f5d319a389ad411f55073d78c48c