perf mem: Fix printing PERF_MEM_LVLNUM_{L2_MHB|MSC}

With commit 8ec9497d3ef34 ("tools/include: Sync uapi/linux/perf.h
with the kernel sources"), 'perf mem report' gives an incorrect memory
access string.
...
0.02% 1 3644 L5 hit [.] 0x0000000000009b0e mlc [.] 0x00007fce43f59480
...

This occurs because, if no entry exists in mem_lvlnum, perf_mem__lvl_scnprintf
will default to 'L%d, lvl', which in this case for PERF_MEM_LVLNUM_L2_MHB is 0x05.
Add entries for PERF_MEM_LVLNUM_L2_MHB and PERF_MEM_LVLNUM_MSC to mem_lvlnum,
so that the correct strings are printed.
...
0.02% 1 3644 L2 MHB hit [.] 0x0000000000009b0e mlc [.] 0x00007fce43f59480
...

Fixes: 8ec9497d3ef34 ("tools/include: Sync uapi/linux/perf.h with the kernel sources")
Suggested-by: Kan Liang <[e-mail]>
Signed-off-by: Thomas Falcon <[e-mail]>
Reviewed-by: Leo Yan <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Namhyung Kim <[e-mail]>

tools/perf/util/mem-events.c

···
 };
 
 static const char * const mem_lvlnum[] = {
+	[PERF_MEM_LVLNUM_L1] = "L1",
+	[PERF_MEM_LVLNUM_L2] = "L2",
+	[PERF_MEM_LVLNUM_L3] = "L3",
+	[PERF_MEM_LVLNUM_L4] = "L4",
+	[PERF_MEM_LVLNUM_L2_MHB] = "L2 MHB",
+	[PERF_MEM_LVLNUM_MSC] = "Memory-side Cache",
 	[PERF_MEM_LVLNUM_UNC] = "Uncached",
 	[PERF_MEM_LVLNUM_CXL] = "CXL",
 	[PERF_MEM_LVLNUM_IO] = "I/O",
···
 		if (mem_lvlnum[lvl])
 			l += scnprintf(out + l, sz - l, mem_lvlnum[lvl]);
 		else
-			l += scnprintf(out + l, sz - l, "L%d", lvl);
+			l += scnprintf(out + l, sz - l, "Unknown level %d", lvl);
 
 		l += scnprintf(out + l, sz - l, " %s", hit_miss);
 		return l;