meta-romulus: Add id-button.bb

This recipe adds the function to assert/deassert identify LED Group
when the ID button is pressed:
1. Add phosphor-gpio-monitor for the ID button GPIO key;
2. Start id-button-pressed.service when the key is pressed;
3. The service starts a script to check the identify LED group state,
   and assert or de-assert it.

Tested: Assert/De-assert identify LED group by pressing the ID button
        on Romulus.

Change-Id: I782dbc15563a313418aa90bee1f48fc97a6d25fb
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/common/recipes-phosphor/gpio/phosphor-gpio-monitor/phosphor-gpio-monitor@.service b/common/recipes-phosphor/gpio/phosphor-gpio-monitor/phosphor-gpio-monitor@.service
index a9644a7..63f88a1 100644
--- a/common/recipes-phosphor/gpio/phosphor-gpio-monitor/phosphor-gpio-monitor@.service
+++ b/common/recipes-phosphor/gpio/phosphor-gpio-monitor/phosphor-gpio-monitor@.service
@@ -4,5 +4,5 @@
 [Service]
 Restart=no
 EnvironmentFile={envfiledir}/obmc/gpio/%I
-ExecStart=/usr/bin/env phosphor-gpio-monitor --path=${{DEVPATH}} --key=${{KEY}} --polarity=${{POLARITY}} --target=${{TARGET}}
+ExecStart=/usr/bin/env phosphor-gpio-monitor --path=${{DEVPATH}} --key=${{KEY}} --polarity=${{POLARITY}} --target=${{TARGET}} --continue=${{CONTINUE}}
 SyslogIdentifier=phosphor-gpio-monitor