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

Presently, platforms such as RD-N2, RD-N2-Cfg1, RD-N2-Cfg2 and RD-V2
utilize nrd_soc_platform_def_v2.h and nrd_soc_css_def_v2.h for all css
and soc-related defines. So move these two header files into a new
directory named 'nrd2'. This new directory will serve as the container
of header files that are specific to the former stated platforms.

Signed-off-by: Rohit Mathew <rohit.mathew@arm.com>
Change-Id: I51ba0944dea91ae81e1840947d2e9af9b28d561d
3 files changed