ARM: 9209/1: Spectre-BHB: avoid pr_info() every time a CPU comes out of idle

Jon reports that the Spectre-BHB init code is filling up the kernel log
with spurious notifications about which mitigation has been enabled,
every time any CPU comes out of a low power state.

Given that Spectre-BHB mitigations are system wide, only a single
mitigation can be enabled, and we already print an error if two types of
CPUs coexist in a single system that require different Spectre-BHB
mitigations.

This means that the pr_info() that describes the selected mitigation
does not need to be emitted for each CPU anyway, and so we can simply
emit it only once.

In order to clarify the above in the log message, update it to describe
that the selected mitigation will be enabled on all CPUs, including ones
that are unaffected. If another CPU comes up later that is affected and
requires a different mitigation, we report an error as before.

Fixes: b9baf5c8 ("ARM: Spectre-BHB workaround")
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>