rdfremont: add platform module for mcpfw

Add an initial implementation of the MCP platform module that indicates
the completion of the MCP RAM boot stage. This module is expected to get
additional functionality in subsequent additions to the MCP RAM
firmware.

Signed-off-by: Shriram K <shriram.k@arm.com>
Change-Id: I16bafa6199f0d90beb8eba6d927c2f8d87692362