perf: Adding sysfs group format attribute for pmu device

Adding sysfs group 'format' attribute for pmu device that
contains a syntax description on how to construct raw events.

The event configuration is described in following
struct pefr_event_attr attributes:

  config
  config1
  config2

Each sysfs attribute within the format attribute group,
describes mapping of name and bitfield definition within
one of above attributes.

eg:
  "/sys/...<dev>/format/event" contains "config:0-7"
  "/sys/...<dev>/format/umask" contains "config:8-15"
  "/sys/...<dev>/format/usr"   contains "config:16"

the attribute value syntax is:

  line:      config ':' bits
  config:    'config' | 'config1' | 'config2"
  bits:      bits ',' bit_term | bit_term
  bit_term:  VALUE '-' VALUE | VALUE

Adding format attribute definitions for x86 cpu pmus.

Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/n/tip-vhdk5y2hyype9j63prymty36@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Documentation/ABI/testing/sysfs-bus-event_source-devices-format

@@ -0,0 +1,14 @@
+Where:		/sys/bus/event_source/devices/<dev>/format
+Date:		January 2012
+Kernel Version: 3.3
+Contact:	Jiri Olsa <jolsa@redhat.com>
+Description:
+		Attribute group to describe the magic bits that go into
+		perf_event_attr::config[012] for a particular pmu.
+		Each attribute of this group defines the 'hardware' bitmask
+		we want to export, so that userspace can deal with sane
+		name/value pairs.
+
+		Example: 'config1:1,6-10,44'
+		Defines contents of attribute that occupies bits 1,6-10,44 of
+		perf_event_attr::config1.