doc: Add a binding document for COT descriptors

Added a binding document for COT descriptors which is going
to be used in order to create COT desciptors at run-time.

Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
Change-Id: Ic54519b0e16d145cd1609274a00b137a9194e8dd
2 files changed