debugfs: add 9p device interface

The 9p interface provides abstraction layers allowing the software
that uses devices to be independent from the hardware.

This patch provides a file system abstraction to link drivers to their
devices and propose a common interface to expose driver operations to
higher layers. This file system can be used to access and configure a
device by doing read/write operations.

Signed-off-by: Ambroise Vincent <ambroise.vincent@arm.com>
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: Ia9662393baf489855dc0c8f389fe4a0afbc9c255
diff --git a/lib/debugfs/debugfs.mk b/lib/debugfs/debugfs.mk
new file mode 100644
index 0000000..030556a
--- /dev/null
+++ b/lib/debugfs/debugfs.mk
@@ -0,0 +1,10 @@
+#
+# Copyright (c) 2019, ARM Limited and Contributors. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#
+
+DEBUGFS_SRCS	:=	$(addprefix lib/debugfs/,	\
+			dev.c				\
+			devc.c				\
+			devroot.c)