scripts: Move logic in prep_benchmarks.sh into a function

This prepares for adding the ability to undo the setup.

Change-Id: Ie3fa3a76715663d9785a1d2f9d88ab20e0d07dce
Signed-off-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-on: https://review.gerrithub.io/393829
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>

scripts/prep_benchmarks.sh

@@ -1,5 +1,6 @@
 #!/usr/bin/env bash
 
+function configure_performance() {
 	echo -n "Placing all CPUs in performance mode..."
 	for governor in /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor; do
 		echo -n performance > $governor
@@ -39,3 +40,6 @@ for queue in /sys/block/nvme*n*/queue; do
 		fi
 	done
 	echo "Done"
+}
+
+configure_performance