FVP: Enable capability to disable auth via dynamic config

This patch adds capability to FVP to disable authentication dynamically
via the `disable_auth` property in TB_FW_CONFIG. Both BL1 and BL2 parses
the TB_FW_CONFIG for the `disable_auth` property and invokes the
`load_dyn_disable_auth()` API to disable authentication if the
property is set to 1. The DYN_DISABLE_AUTH is enabled by default for
FVP as it is a development platform. Note that the TB_FW_CONFIG has to
be authenticated by BL1 irrespective of these settings.

The arm_bl2_dyn_cfg_init() is now earlier in bl2_plat_preload_setup()
rather than in bl2_platform_setup() as we need to get the value of
`disable_auth` property prior to authentication of any image by BL2.

Change-Id: I734acd59572849793e5020ec44c6ac51f654a4d1
Signed-off-by: Soby Mathew <soby.mathew@arm.com>
diff --git a/plat/arm/common/arm_common.mk b/plat/arm/common/arm_common.mk
index 1218548..4b23ac6 100644
--- a/plat/arm/common/arm_common.mk
+++ b/plat/arm/common/arm_common.mk
@@ -157,7 +157,6 @@
 				drivers/io/io_memmap.c				\
 				drivers/io/io_storage.c				\
 				plat/arm/common/arm_bl1_setup.c			\
-				plat/arm/common/arm_dyn_cfg.c			\
 				plat/arm/common/arm_err.c			\
 				plat/arm/common/arm_io_storage.c
 ifdef EL3_PAYLOAD_BASE
@@ -177,11 +176,15 @@
 
 # Add `libfdt` and Arm common helpers required for Dynamic Config
 include lib/libfdt/libfdt.mk
-BL2_SOURCES		+=	plat/arm/common/arm_dyn_cfg.c		\
+
+DYN_CFG_SOURCES		+=	plat/arm/common/arm_dyn_cfg.c		\
 				plat/arm/common/arm_dyn_cfg_helpers.c	\
 				common/fdt_wrappers.c			\
 				${LIBFDT_SRCS}
 
+BL1_SOURCES		+=	${DYN_CFG_SOURCES}
+BL2_SOURCES		+=	${DYN_CFG_SOURCES}
+
 ifeq (${BL2_AT_EL3},1)
 BL2_SOURCES		+=	plat/arm/common/arm_bl2_el3_setup.c
 endif