feat(tc): get the parent component provided DPE context_handle

Each client who wants to communicate with the DPE service
must own a valid context handle issued by the DPE service.
A context handle can be used for a single time then it will
be invalidated by the DPE service. In case of calls from
the same component, the next valid context handle is
returned in the response to a DPE command. When a component
finishes their job then the next component in the boot flow
inherits its first context handle from its parent.
How the inheritance is done can be client or
platform-dependent. It can be shared through shared
memory or be part of a DTB object passed to the next
bootloader stage.

Signed-off-by: Tamas Ban <tamas.ban@arm.com>
Signed-off-by: David Vincze <david.vincze@arm.com>
Change-Id: Ic82f074f1c5b15953e78f9fa5404ed7f48674cbb
5 files changed