Split include/Makefile.am content into subdirs

When someone is modifying a given library there's no need to be looking
at a common file contains tons of lines from different libraries.
Furthermore, this removes the need of "nobase" autofoo prefix, hence
following the usual directive of having one Makefile per directory.

Change-Id: I785891c2f89114bf8303c799094b637d3d25ac71
diff --git a/include/osmocom/ctrl/Makefile.am b/include/osmocom/ctrl/Makefile.am
new file mode 100644
index 0000000..416e3ab
--- /dev/null
+++ b/include/osmocom/ctrl/Makefile.am
@@ -0,0 +1,13 @@
+osmoctrl_HEADERS = \
+	control_cmd.h \
+	control_if.h \
+	ports.h \
+	$(NULL)
+
+if ENABLE_VTY
+osmoctrl_HEADERS += \
+	control_vty.h \
+	$(NULL)
+endif
+
+osmoctrldir = $(includedir)/osmocom/ctrl