This adds a --enable-systemtap configure option, which will then
add static tracepoints to the generated osmo-bts-* binary.
At this point, only two sets of tracepoints are supported, and
only in osmo-bts-trx: ul_data_{start,done} and dl_rts_{start,done}.
The probes are intended to be used for analyzing the amount of time
needed for processing of uplink bursts / generation of downlink bursts.
Change-Id: Ibb4962253f1a195dc1a54405bac058ccb2545799
