perf/x86/intel: Mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch
cases where we are expecting to fall through.

This patch fixes the following warnings:

  arch/x86/events/intel/core.c: In function ‘intel_pmu_init’:
  arch/x86/events/intel/core.c:4959:8: warning: this statement may fall through [-Wimplicit-fallthrough=]
  arch/x86/events/intel/core.c:5008:8: warning: this statement may fall through [-Wimplicit-fallthrough=]

Warning level 3 was used: -Wimplicit-fallthrough=3

This patch is part of the ongoing efforts to enable -Wimplicit-fallthrough.
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190624161913.GA32270@embeddedorSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/events/intel/core.c

@@ -4954,6 +4954,7 @@ __init int intel_pmu_init(void)
 
 	case INTEL_FAM6_SKYLAKE_X:
 		pmem = true;
+		/* fall through */
 	case INTEL_FAM6_SKYLAKE_MOBILE:
 	case INTEL_FAM6_SKYLAKE_DESKTOP:
 	case INTEL_FAM6_KABYLAKE_MOBILE:
@@ -5003,6 +5004,7 @@ __init int intel_pmu_init(void)
 	case INTEL_FAM6_ICELAKE_X:
 	case INTEL_FAM6_ICELAKE_XEON_D:
 		pmem = true;
+		/* fall through */
 	case INTEL_FAM6_ICELAKE_MOBILE:
 	case INTEL_FAM6_ICELAKE_DESKTOP:
 		x86_pmu.late_ack = true;