lisa._kmod: Add util_est_unified trace events
Created by: honxia02
FEATURE
Upstream has now removed struct util_est and effectively merged util_est.enqueued and util_est.ewma in a single int field. Provide a new trace event for it so the new kernel can trace it.
This also fixes LISA not being able to compile and load the module on the new kernel. We detect whether struct util_est exists to decide if the new signal should be used.