KVM: nVMX: Introduce helpers to check if Hyper-V evmptr12 is valid/set

In order to get rid of raw 'vmx->nested.hv_evmcs_vmptr' accesses when
!CONFIG_KVM_HYPERV, introduce a pair of helpers:

nested_vmx_is_evmptr12_valid() to check that eVMPTR points to a valid
address.

nested_vmx_is_evmptr12_valid() to check that eVMPTR either points to a
valid address or is in 'pending' port-migration state (meaning it is
supposed to be valid but the exact address wasn't acquired from guest's
memory yet).

No functional change intended.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Tested-by: Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>
Link: https://lore.kernel.org/r/20231205103630.1391318-14-vkuznets@redhat.com


Signed-off-by: Sean Christopherson <seanjc@google.com>