plat(rdfremont): add initial suppport for rdfremont platform

Provide initial support for RD-Fremont platform. Add cold and
warm boot routines. Implementation for AEM-FVP is already added
in (commit: TF-RMM Release v0.1.0) Since it applies for rdfremont,
reuse it. Add a RD-Fremont platform specific config file which will
be used to obtain values of build time environment variable.

Signed-off-by: Sathyam Panda <sathyam.panda@arm.com>
Signed-off-by: Vivek Gautam <vivek.gautam@arm.com>
Change-Id: I9b4f28fcccdb7e96252bf35688d98792915dd3cb