handler: Add check for file existence for BM mode

/tmp/BMReady.flag indicates that we are in BM mode.

Tested:
Verified both cases -
- Mar 21 11:17:52 ipmid[1130]: /tmp/BMReady.flag exists so we must be in BM mode
- Mar 21 10:37:04 ipmid[1076]: Unable to find /tmp/BMReady so we must not be in BM mode

Signed-off-by: Brandon Kim <brandonkim@google.com>
Change-Id: I9fa99b40afea7e48ce7e1f9c47e8f081b71b897f
diff --git a/meson.build b/meson.build
index 6384f73..578638b 100644
--- a/meson.build
+++ b/meson.build
@@ -19,6 +19,7 @@
 
 bm_conf_data = configuration_data()
 bm_conf_data.set10('BARE_METAL', get_option('bare_metal'))
+bm_conf_data.set_quoted('BM_SIGNAL_PATH', get_option('bm-signal-path'))
 bm_conf_h = configure_file(
   output: 'bm_config.h',
   configuration: bm_conf_data)