refactor(sgi): move apis and types to nrd prefix

Currently, functions and types internal to neoverse_rd platforms are
named with "sgi" as the prefix. Since common code and platforms are no
longer under the "sgi" umbrella, move the prefix to "nrd". This change
would amend the prefixes for functions, types and objects.

Signed-off-by: Rohit Mathew <Rohit.Mathew@arm.com>
Change-Id: I1080259b661081c535ab46f61df9e4563420bdb0