powerpc/perf: Add stalled-cycles events

Support for stalled-cycles-frontend and stalled-cycles-backend is
added for e500-based processors.

The following mappings are used:

stalled-cycles-frontend or idle-cycles-frontend:
Com:18 Cycles decode stalled

stalled-cycles-backend or idle-cycles-backend
Com:19 cycles issue stalled

Signed-off-by: Chris Freehill <[e-mail]>
Signed-off-by: Benjamin Herrenschmidt <[e-mail]>

arch/powerpc/perf/e500-pmu.c

···
 	[PERF_COUNT_HW_CACHE_MISSES] = 41, /* Data L1 cache reloads */
 	[PERF_COUNT_HW_BRANCH_INSTRUCTIONS] = 12,
 	[PERF_COUNT_HW_BRANCH_MISSES] = 15,
+	[PERF_COUNT_HW_STALLED_CYCLES_FRONTEND] = 18,
+	[PERF_COUNT_HW_STALLED_CYCLES_BACKEND] = 19,
 };
 
 #define C(x)	PERF_COUNT_HW_CACHE_##x