ARM: 8751/1: Add support for Cortex-R8 processor

Cortex-R8 has identical initialisation requirements to Cortex-R7, so
hook it up in proc-v7.S in the same way.

Signed-off-by: Luca Scalabrino <luca.scalabrino@arm.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>