KVM: nVMX: Rename vmcs_to_field_offset{,_table}

vmcs_to_field_offset{,_table} may sound misleading as VMCS is an opaque
blob which is not supposed to be accessed directly. In fact,
vmcs_to_field_offset{,_table} are related to KVM defined VMCS12 structure.

Rename vmcs_field_to_offset() to get_vmcs12_field_offset() for clarity.

No functional change intended.

Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20220112170134.1904308-4-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>