meson: Add subprojects file

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: I7a764691f1d5b68844a19edfeb1c9e30d4412487
diff --git a/subprojects/phosphor-snmp.wrap b/subprojects/phosphor-snmp.wrap
new file mode 100644
index 0000000..58e8441
--- /dev/null
+++ b/subprojects/phosphor-snmp.wrap
@@ -0,0 +1,6 @@
+[wrap-git]
+url = https://github.com/openbmc/phosphor-snmp.git
+revision = HEAD
+
+[provide]
+phosphor-snmp = phosphor_snmp_dep