fix(plat/fvp): allow changing the kernel DTB load address

We currently use ARM_PRELOADED_DTB_BASE build
variable to pass the kernel DTB base address to
the kernel when using the ARM_LINUX_KERNEL_AS_BL33
option. However this variable doesn't actually
change the DTB load address.

The DTB load address is actually specified in the
FW_CONFIG DTS (fvp_fw_config.dts) as 'hw_config'.
This patch passes the hw_config value instead of
ARM_PRELOADED_DTB_BASE allowing us to change
the kernel DTB load address through
fvp_fw_config.dts.

With this change we don't need the ARM_PRELOADED_DTB_BASE
build variable if RESET_TO_BL31 is not set.
Note that the hw_config value needs to be within the
ARM_DTB_DRAM_NS region specified by FVP_DTB_DRAM_MAP_START
and FVP_DTB_DRAM_MAP_SIZE.

This patch also expands the ARM_DTB_DRAM_NS region to 32MB.

Signed-off-by: Zelalem Aweke <zelalem.aweke@arm.com>
Change-Id: Idd74cdf5d2c649bb320644392ba5d69e175a53a9
diff --git a/plat/arm/common/arm_bl31_setup.c b/plat/arm/common/arm_bl31_setup.c
index d760312..d131bb9 100644
--- a/plat/arm/common/arm_bl31_setup.c
+++ b/plat/arm/common/arm_bl31_setup.c
@@ -218,7 +218,11 @@
 	 * tree blob (DTB) in x0, while x1-x3 are reserved for future use and
 	 * must be 0.
 	 */
+#if RESET_TO_BL31
 	bl33_image_ep_info.args.arg0 = (u_register_t)ARM_PRELOADED_DTB_BASE;
+#else
+	bl33_image_ep_info.args.arg0 = (u_register_t)hw_config;
+#endif
 	bl33_image_ep_info.args.arg1 = 0U;
 	bl33_image_ep_info.args.arg2 = 0U;
 	bl33_image_ep_info.args.arg3 = 0U;