trivial: Fix compiler warnings

- Add missing return statements
- Add missing const modifiers
- Initialize variables correctly
- Remove unused variables
- Correct incorrect type definitions
- Use correct printf format string types

ClockServer: Refactor client-server interface

Use the connector definitions to control interface configuration and
initialization.

Provide an ADL API for creating the ClockServer client-server interface
in any component.

ClockServer: Change error codes, add diagnostics

This changes the error return codes to conform more to our standards of
error codes being negative instead of positive. Also add in error
diagnostic messages to help the user investigate errors.

ClockServer,tx2: Add BPMP connector definitions

Instead of initialising the BPMP component alongside the ClockServer,
this commit changes it so that the user has to instantiate an instance
of the BPMPServer and connect it to the ClockServer.

Also, this commit also adds a platform specific initialisation function
to allow platform specific initialisation procedures to be carried out
before initialising the clock drivers. For the tx2, this involves
creating a BPMP interface using the BPMPServer server library and
registering it with the interface registration service so that clock
driver can find it and use it.

components: Add ClockServer component

The ClockServer component is a new component that is responsible for
managing and multiplexing requests to the clock controllers of a
particular platform. The functionality of the component is very limited
at the moment and can only support the functionality that is exposed via
the clock subsystem in libplatsupport. There is no access control
with regards to clock gates so components can interfere with other
components by manipulating the clock gates.