Currently, whenever an erratum workaround is enabled, it will be
applied whether or not the erratum is relevent for the CPU.  This
patch changes this - we check the variant and revision fields in the
main ID register to determine which errata to apply.

We also avoid re-applying erratum 460075 if it has already been applied.
Applying this fix in non-secure mode results in the kernel failing to
boot (or even do anything.)

This fixes booting on some ARMv7 based platforms which otherwise
silently fail.
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>