doc: Update CoT binding to make it more generic
doc: Update CoT binding to make it more generic

Updated the CoT binding document to show chain of trust relationship
with the help of 'authentication method' and 'authentication data'
instead of showing content of certificate and fixed rendering issue
while creating html page using this document.

Signed-off-by: Manish V Badarkhe <d2342ad575f6bc1a5f5a5b89d6db0f72dd7e0e4c@arm.com>
Change-Id: Ib48279cfe786d149ab69ddc711caa381a50f9e2b

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware