powerpc/perf/hv-24x7: parse catalog and populate sysfs with events

Retrieves and parses the 24x7 catalog on POWER systems that supply it
(right now, only POWER 8). Events are exposed via sysfs in the standard
fashion, and are all parameterized.

	$ cd /sys/bus/event_source/devices/hv_24x7/events

	$ cat HPM_CS_FROM_L4_LDATA__PHYS_CORE
	domain=0x2,offset=0xd58,core=?,lpar=0x0

	$ cat HPM_TLBIE__VCPU_HOME_CHIP
	domain=0x4,offset=0x358,vcpu=?,lpar=?

where user is required to specify values for the fields with '?' (like
core, vcpu, lpar above), when specifying the event with the perf tool.

Catalog is (at the moment) only parsed on boot. It needs re-parsing
when a some hypervisor events occur. At that point we'll also need to
prevent old events from continuing to function (counter that is passed
in via spare space in the config values?).

Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>