refactor(sgi): rename "CSS_SGI"" macro prefixes to "NRD"

As of now, several internal macros utilize "CSS_SGI" as their prefix.
Given the change to neoverse_rd, and the subsequent migration out of the
css directory, the prefix "CSS_SGI" is no longer appropriate.
Therefore, update the macro prefixes to "NRD" for consistency and
clarity.

Signed-off-by: Rohit Mathew <Rohit.Mathew@arm.com>
Change-Id: I3d1a9dba3e83f6e107379fc5bcf8256cc93d8c3d
25 files changed