build: add wrapfiles for dependencies

Update meson.build and add wrapfiles so that all dependencies
are handled as subprojects.  This allows builds completely
outside of bitbake or an SDK.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Id9e46013671d1d407b13549c29c15770c1c6fb2c
diff --git a/subprojects/sdeventplus.wrap b/subprojects/sdeventplus.wrap
new file mode 100644
index 0000000..085bb5e
--- /dev/null
+++ b/subprojects/sdeventplus.wrap
@@ -0,0 +1,3 @@
+[wrap-git]
+url = https://github.com/openbmc/sdeventplus.git
+revision = HEAD