phosphor-mboxd: Define mboxd dbus properties and methods

Defines the mboxd yaml file, as the first change
to allow phosphor-mboxd to use sdbusplus.
Modifies gitignore to ignore mboxd binary but not
the mboxd directory in the yaml's path.
Describes the xyz.openbmc_project.Mboxd interface

Change-Id: Iec2876b93b5152b1fafdbefce277fcf64b9525f8
Signed-off-by: Leonel Gonzalez <lgonzalez@us.ibm.com>
diff --git a/.gitignore b/.gitignore
index 9523617..e87701d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -47,7 +47,7 @@
 Makefile
 .deps
 arm-openbmc-linux-gnueabi-libtool
-mboxd
+/mboxd
 mboxctl
 cscope.out
 /test/*.o