fix: rename Matterhorn, Matterhorn ELP, and Klein CPUs

This patch renames the Matterhorn, Matterhorn ELP, and Klein CPUs to
Cortex A710, Cortex X2, and Cortex A510 respectively.

Signed-off-by: John Powell <john.powell@arm.com>
Change-Id: I056d3114210db71c2840a24562b51caf2546e195
15 files changed