perf/POWER7: Create a sysfs format entry for Power7 events

Create a sysfs entry, '/sys/bus/event_source/devices/cpu/format/event'
which describes the format of the POWER7 PMU events.

This code is based on corresponding code in x86.

Changelog[v4]:  [Michael Ellerman, Paul Mckerras] The event format is different
		for other POWER cpus. So move the code to POWER7-specific,
		power7-pmu.c Also, the POWER7 format uses bits 0-19 not 0-20.

Changelog[v2]: [Jiri Osla] Use PMU_FORMAT_ATTR rather than duplicating code.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Acked-by: Paul Mackerras <paulus@samba.org>
Tested-by: Michael Ellerman <michael@ellerman.id.au>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Anton Blanchard <anton@au1.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Michael Ellerman <michael@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Robert Richter <robert.richter@amd.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: benh@kernel.crashing.org
Cc: linuxppc-dev@ozlabs.org
Link: http://lkml.kernel.org/r/20130306054826.GA14627@us.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>