rdn1e1: Rename clark to rdn1e1

SGI-Clark has two configurations: one with Ares cores, and another with
Helios cores, which have been given the official product names
Neoverse N1 and E1 respectively.

This patch renames the clark product to better reflect these names,
becoming rdn1e1.

Change-Id: Ibdec9f03fdf4e76ee3ba2badb86e463a631f1938
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>