KVM: pfncache: remove unnecessary exports

KVM: pfncache: remove unnecessary exports

There is no need for the existing kvm_gpc_XXX() functions to be exported.
Clean up now before additional functions are added in subsequent patches.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
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Cc: Sean Christopherson <seanjc@google.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
v8:
 - New in this version.