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/bl31/bl31.mk b/bl31/bl31.mk
index c9ba926..85d471c 100644
--- a/bl31/bl31.mk
+++ b/bl31/bl31.mk
@@ -43,6 +43,11 @@
 BL31_SOURCES		+=	lib/pmf/pmf_main.c
 endif
 
+include lib/debugfs/debugfs.mk
+ifeq (${USE_DEBUGFS},1)
+	BL31_SOURCES	+= $(DEBUGFS_SRCS)
+endif
+
 ifeq (${EL3_EXCEPTION_HANDLING},1)
 BL31_SOURCES		+=	bl31/ehf.c
 endif