Fix broken links to various sections across docs

These broken links were found with the help of this command:
$> sphinx-build -M linkcheck . build

A sample broken link is reported as follows:
(line   80) -local-   firmware-design.rst#secure-el1-payloads-and-dispatchers

Change-Id: I5dcefdd4b8040908658115647e957f6c2c5da7c2
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
diff --git a/docs/plat/arm/fvp/index.rst b/docs/plat/arm/fvp/index.rst
index fd658bb..745e31f 100644
--- a/docs/plat/arm/fvp/index.rst
+++ b/docs/plat/arm/fvp/index.rst
@@ -635,7 +635,7 @@
 
 *Copyright (c) 2019-2020, Arm Limited. All rights reserved.*
 
-.. _TB_FW_CONFIG for FVP: ../plat/arm/board/fvp/fdts/fvp_tb_fw_config.dts
+.. _TB_FW_CONFIG for FVP: https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git/tree/plat/arm/board/fvp/fdts/fvp_tb_fw_config.dts
 .. _Arm's website: `FVP models`_
 .. _FVP models: https://developer.arm.com/products/system-design/fixed-virtual-platforms
 .. _Linaro Release 19.06: http://releases.linaro.org/members/arm/platforms/19.06