KVM: selftests: Add "arch" to common utils that have arch implementations

Add "arch" into the name of utility functions that are declared in common
code, but (surprise!) have arch-specific implementations.  Shuffle code
around so that all such helpers' declarations are bundled together.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>