perf/x86/intel/uncore: Support extra IMC channel on Ice Lake server

There are three channels on a Ice Lake server, but only two channels
will ever be active. Current perf only enables two channels.

Support the extra IMC channel, which may be activated on some Ice Lake
machines. For a non-activated channel, the SW can still access it. The
write will be ignored by the HW. 0 is always returned for the reading.

Fixes: 2b3b76b5 ("perf/x86/intel/uncore: Add Ice Lake server uncore support")
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/1629991963-102621-2-git-send-email-kan.liang@linux.intel.com