Attention handler configuration file support

The default behavior of the attention handler can be overriden by
modifying the config file contents. The behavior can also be defined
by the associated build option. The default behavior remains
unchanged. The intent of this change is to allow other components to
change the attention handler behavior by updating the configuration file
and restarting the attention handler service.

Signed-off-by: Ben Tyner <ben.tyner@ibm.com>
Change-Id: I8f73004c926a3a070c5feb690ee5684429f922c5
diff --git a/meson_options.txt b/meson_options.txt
index 635fb07..5587317 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -1,7 +1,7 @@
-option('tests', type: 'feature', description: 'Build tests')
-option('nlmode', type: 'feature', description: 'no run-time control')
-
-option('phal', type: 'feature', value : 'disabled',
+option('tests', type : 'feature', description : 'Build tests')
+option('nlmode', type : 'feature', description : 'no run-time control')
+option('phal', type : 'feature', value : 'disabled',
         description : '''Enable PHAL APIs for retrieving data from the POWER
                          Systems device tree''')
-
+option('attn_config', type : 'string', value : '',
+        description : '''Attention handler default configuration override''')