refactor(sgi): update comment references to "sgi platform"

As part of the move from "sgi", rename all comments referencing "sgi
platform" to "Neoverse RD platform".

Signed-off-by: Rohit Mathew <Rohit.Mathew@arm.com>
Change-Id: Ic72d6080cc74baaf40510e04d56926cdb5712311
3 files changed