ARM: enable ARM errata 643719 workaround by default

The effects of not having ARM errata 643719 enabled on affected CPUs
can be very confusing and hard to debug.  Rather than leave this to
chance, enable this workaround by default.  Now that we have rearranged
the code, it should have a low impact on the majority of CPUs.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>