refactor(sgi): replace references to "SGI"/"sgi" for neoverse_rd

Currently, there are several reference to "SGI" or "sgi" in comments or
as macro prefix within the neoverse_rd directory. As part of the
migration to neoverse_rd, rename all occurences of "SGI/sgi" to
"Neoverse-RD" or the "NRD" prefix accordingly. All references in
comments are rephrased as "Neoverse RD platforms". References in code
are renamed as "NRD"/"nrd" accordingly.

Signed-off-by: Rohit Mathew <Rohit.Mathew@arm.com>
Change-Id: I55bdab01051974b3ddb2dae3bc4c0e253fb85fc3
6 files changed