kvm/i386: make kvm_filter_msr() and related definitions private to kvm module

kvm/i386: make kvm_filter_msr() and related definitions private to kvm module

kvm_filer_msr() is only used from i386 kvm module. Make it static so that its
easy for developers to understand that its not used anywhere else.
Same for QEMURDMSRHandler, QEMUWRMSRHandler and KVMMSRHandlers definitions.

CC: philmd@linaro.org
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Ani Sinha <anisinha@redhat.com>
Link: https://lore.kernel.org/r/20240903140045.41167-1-anisinha@redhat.com
[Make struct unnamed. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>