meson: Add subprojects file

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: Ie2cf5f445e7939ce394a43ae2a59901e1550ff53
diff --git a/subprojects/phosphor-objmgr.wrap b/subprojects/phosphor-objmgr.wrap
new file mode 100644
index 0000000..6e41898
--- /dev/null
+++ b/subprojects/phosphor-objmgr.wrap
@@ -0,0 +1,6 @@
+[wrap-git]
+url = https://github.com/openbmc/phosphor-objmgr
+revision = HEAD
+
+[provide]
+libmapper = mapper_dep