ARM: proc-v7: avoid errata 430973 workaround for non-Cortex A8 CPUs

Avoid the errata 430973 workaround for non-Cortex A8 CPUs.  Having this
workaround enabled introduces an additional branch target buffer flush
into the context switching path, something we wish to avoid.  To allow
this errata to be enabled in multiplatform kernels while reducing its
impact, rearrange the Cortex-A8 CPU support to avoid impacting on other
Version 7 CPUs.

Tested-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>