cxl/test: Add generic mock events

Facilitate testing basic Get/Clear Event functionality by creating
multiple logs and generic events with made up UUID's.

Data is completely made up with data patterns which should be easy to
spot in trace output.

A single sysfs entry resets the event data and triggers collecting the
events for testing.

Test traces are easy to obtain with a small script such as this:

	#!/bin/bash -x

	devices=`find /sys/devices/platform -name cxl_mem*`

	# Turn on tracing
	echo "" > /sys/kernel/tracing/trace
	echo 1 > /sys/kernel/tracing/events/cxl/enable
	echo 1 > /sys/kernel/tracing/tracing_on

	# Generate fake interrupt
	for device in $devices; do
	        echo 1 > $device/event_trigger
	done

	# Turn off tracing and report events
	echo 0 > /sys/kernel/tracing/tracing_on
	cat /sys/kernel/tracing/trace

Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Link: https://lore.kernel.org/r/20221216-cxl-ev-log-v7-6-2316a5c8f7d8@intel.com


Signed-off-by: Dan Williams <dan.j.williams@intel.com>