ARM: 7196/1: errata: Remove SMP dependency for erratum 720789

Activation conditions for a workaround should not be encoded in the
workaround's direct dependencies if this makes otherwise reasonable
configuration choices impossible.

The workaround for erratum 720789 only affects a code path which is
not active in UP kernels; hence it should be safe to turn on in UP
kernels, without penalty.

This patch simply removes the extra dependency on SMP from Kconfig.

This means that configs for buggy silicon can simply select
ARM_ERRATA_720789, without preventing a UP kernel from being built
or duplicatiing knowledge about when to activate the workaround.

Signed-off-by: Dave Martin <dave.martin@linaro.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>