KVM: arm64: Move handle check into pkvm_pgtable_stage2_destroy_range()

KVM: arm64: Move handle check into pkvm_pgtable_stage2_destroy_range()

When pKVM is enabled, a VM has a 'handle' allocated by the hypervisor
in kvm_arch_init_vm() and released later by kvm_arch_destroy_vm().

Consequently, the only time __pkvm_pgtable_stage2_unmap() can run into
an uninitialised 'handle' is on the kvm_arch_init_vm() failure path,
where we destroy the empty stage-2 page-table if we fail to allocate a
handle.

Move the handle check into pkvm_pgtable_stage2_destroy_range(), which
will additionally handle protected VMs in subsequent patches.

Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Tested-by: Mostafa Saleh <smostafa@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
Link: https://patch.msgid.link/20260330144841.26181-4-will@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>