refactor(neoverse-rd): header files for first generation platforms

Presently, platforms such as SGI-575, RD-N1-Edge single and dual chip,
RD_V1 single and multi-chip utilize nrd_soc_platform_def.h and
nrd_soc_css_def.h for all css and soc-related defines. So move these
two header files into a new directory named 'nrd1'. This new directory
will serve as the container of header files that are specific to
SGI-575, RD-N1 and RD-V1 platform and its variants.

Signed-off-by: Rohit Mathew <rohit.mathew@arm.com>
Change-Id: I9d70659c6f5000ad6c1cfc0738f9e81f03238f5f
6 files changed