feat(arm): add support for loading CONFIG from BL2

This commit introduces a new ARM platform-specific build option called
`ARM_FW_CONFIG_LOAD_ENABLE`. This option enables the loading of the
`fw_config` device tree when resetting to the BL2 scenario.

Additionally, the FW_CONFIG image reference has been added to the
fdts/tbbr_cot_descriptors.dtsi file in order to use in the scenario of
RESET_TO_BL2.

Signed-off-by: Divin Raj <divin.raj@arm.com>
Change-Id: I11de497b7dbb1386ed84d939d6fd2a11856e9e1b
diff --git a/fdts/tbbr_cot_descriptors.dtsi b/fdts/tbbr_cot_descriptors.dtsi
index b3c0ca7..253297f 100644
--- a/fdts/tbbr_cot_descriptors.dtsi
+++ b/fdts/tbbr_cot_descriptors.dtsi
@@ -195,6 +195,12 @@
 			hash = <&hw_config_hash>;
 		};
 
+		fw_config {
+			image-id = <FW_CONFIG_ID>;
+			parent = <&trusted_boot_fw_cert>;
+			hash = <&fw_config_hash>;
+		};
+
 		scp_bl2_image {
 			image-id = <SCP_BL2_IMAGE_ID>;
 			parent = <&scp_fw_content_cert>;