build: fix build with disabled test modules

install: cannot stat 'testsuite/module-playground/mod-loop-f.ko': No
such file or directory
Makefile:2881: recipe for target 'rootfs' failed
make[1]: *** [rootfs] Error 1
make[1]: *** Waiting for unfinished jobs....
Makefile:2101: recipe for target 'check-recursive' failed

We need to ship pre-compiled binaries so it's possible to run
"make check" on servers without kernel headers.

Also add them to EXTRA_DIST as other sources.
diff --git a/Makefile.am b/Makefile.am
index d4eeb7e..981a1af 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -285,6 +285,8 @@
 	testsuite/module-playground/mod-loop-c.c \
 	testsuite/module-playground/mod-loop-d.c \
 	testsuite/module-playground/mod-loop-e.c \
+	testsuite/module-playground/mod-loop-f.c \
+	testsuite/module-playground/mod-loop-g.c \
 	testsuite/module-playground/mod-loop.h \
 	testsuite/module-playground/mod-simple.c \
 	testsuite/module-playground/mod-simple-i386.ko \