BUILD: traces: add USE_TRACE allowing to disable traces

BUILD: traces: add USE_TRACE allowing to disable traces

This reduces the total code size by 6-10% and speeds up the build a
bit. It can be further reduced by disabling the trace decoding code
inside certain subsystems like muxes. But at least like this it will
help users on small systems to reduce the footprint when not needed
by explicitly passing USE_TRACE=0 (they remain enabled by default).