build: Cleanup subprojects and gitignore

Change-Id: I4bb3d962214084127013adf6eb9012675a614bca
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/.gitignore b/.gitignore
index 327ea97..ae2d61d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,9 @@
 /build*/
-/subprojects/*/
+/subprojects/*
+!/subprojects/googletest.wrap
+!/subprojects/nlohmann_json.wrap
+!/subprojects/phosphor-dbus-interfaces.wrap
+!/subprojects/phosphor-logging.wrap
+!/subprojects/sdbusplus.wrap
+!/subprojects/sdeventplus.wrap
+!/subprojects/stdplus.wrap