perf/x86/uncore: use MiB unit for events for SNB/IVB/HSW IMC

perf/x86/uncore: use MiB unit for events for SNB/IVB/HSW IMC

This patch makes perf use Mebibytes to display the counts
of uncore_imc/data_reads/ and uncore_imc/data_writes.

1MiB = 1024*1024 bytes.

Cc: mingo@elte.hu
Cc: acme@redhat.com
Cc: ak@linux.intel.com
Cc: zheng.z.yan@intel.com
Cc: peterz@infradead.org
Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1392132015-14521-9-git-send-email-eranian@google.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>