selftests/resctrl: Add MBM test

MBM (Memory Bandwidth Monitoring) test is the first implemented selftest.
It starts a stressful memory bandwidth benchmark and assigns the
bandwidth pid in a resctrl monitoring group. Read and compare perf IMC
counter and MBM total bytes for the benchmark. The numbers should be
close enough to pass the test.

Default benchmark is built-in fill_buf. But users can specify their
own benchmark by option "-b".

We can add memory bandwidth monitoring for multiple processes in the
future.

Co-developed-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Co-developed-by: Babu Moger <babu.moger@amd.com>
Signed-off-by: Babu Moger <babu.moger@amd.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/resctrl/Makefile

@@ -3,10 +3,15 @@ CFLAGS = -g -Wall
 SRCS=$(wildcard *.c)
 OBJS=$(SRCS:.c=.o)
 
+all: resctrl_tests
+
 $(OBJS): $(SRCS)
 	$(CC) $(CFLAGS) -c $(SRCS)
 
+resctrl_tests: $(OBJS)
+	$(CC) $(CFLAGS) -o $@ $^
+
 .PHONY: clean
 
 clean:
-	$(RM) $(OBJS)
+	$(RM) $(OBJS) resctrl_tests