perf list: Add metrics to command line usage

Before:

Usage: perf list [<options>] [hw|sw|cache|tracepoint|pmu|sdt|event_glob]

After:

Usage: perf list [<options>] [hw|sw|cache|tracepoint|pmu|sdt|metric|metricgroup|event_glob]

Committer testing:

Before and after we get these outputs on a Lenovo t480s (i7-8650U):

# perf list metricgroup

List of pre-defined events (to be used in -e):

Metric Groups:

BrMispredicts
BrMispredicts_SMT
Branches
Cache_Misses
DSB
FLOPS
FLOPS_SMT
Fetch_BW
IcMiss
Instruction_Type
Memory_BW
Memory_Bound
Memory_Lat
No_group
PGO
Pipeline
Power
Retire
SMT
Summary
TLB
TLB_SMT
TopDownL1
TopDownL1_SMT
TopdownL1
TopdownL1_SMT
#

# perf list metric | head -11

Metrics:

Backend_Bound
[This category represents fraction of slots where no uops are being delivered due to a lack of required resources for accepting new uops in the Backend]
Backend_Bound_SMT
[This category represents fraction of slots where no uops are being delivered due to a lack of required resources for accepting new uops in the Backend. SMT version; use when SMT is enabled and measuring per logical CPU]
Bad_Speculation
[This category represents fraction of slots wasted due to incorrect speculations]
Bad_Speculation_SMT
[This category represents fraction of slots wasted due to incorrect speculations. SMT version; use when SMT is enabled and measuring per logical CPU]
#

Signed-off-by: Ian Rogers <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Stephane Eranian <[e-mail]>
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/builtin-list.c

···
 		OPT_END()
 	};
 	const char * const list_usage[] = {
-		"perf list [<options>] [hw|sw|cache|tracepoint|pmu|sdt|event_glob]",
+		"perf list [<options>] [hw|sw|cache|tracepoint|pmu|sdt|metric|metricgroup|event_glob]",
 		NULL
 	};