perf/x86/intel/uncore: Support CoffeeLake 8th CBOX

Coffee Lake has 8 core products which has 8 Cboxes. The 8th CBOX is
mapped into different MSR space.

Increase the num_boxes to 8 to handle the new products. It will not
impact the previous platforms, SkyLake, KabyLake and earlier CoffeeLake.
Because the num_boxes will be recalculated in uncore_cpu_init and
doesn't exceed the x86_max_cores.

Introduce a new box flag bit to indicate the 8th CBOX.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: http://lkml.kernel.org/r/20181019170419.378-2-kan.liang@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>