tools: add gen-eventfilter.py

Generate event filtering code for lg2::commit from an input json
file, so that system integrators can create default filtering rules
to omit undesired events and errors from their systems.

Tested:

Used `log-create` to create an event and observed it.  Modified the
default event filter as follows and saw log was not created.

```
@@ -3,6 +3,9 @@
         "default": "allowed"
     },
     "errors": {
-        "default": "allowed"
+        "default": "allowed",
+        "ids": [
+            "xyz.openbmc_project.State.SMC.SMCFailed"
+        ]
     }
 }
```

```
$ ./builddir/log-create xyz.openbmc_project.State.SMC.SMCFailed --json '{ "IDENTIFIER": "/xyz/openbmc_project/inventory/SomeSMC", "FAILURE_TYPE": "Timeout for the SMC" }'
```

Change-Id: Ib6041481075758b994bb27a816dbf5e9f26c2841
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/tools/meson.build b/tools/meson.build
index bb08ffb..fcde0bf 100644
--- a/tools/meson.build
+++ b/tools/meson.build
@@ -1,4 +1,7 @@
 tool_dir = meson.current_source_dir()
 
 elog_gen = files('elog-gen.py')
+eventfilter_gen = files('gen-eventfilter.py')
+default_eventfilter_json = files('phosphor-logging/default-eventfilter.json')
+
 subdir('phosphor-logging/templates')