KVM: account allocation in generic version of kvm_arch_alloc_vm()

Account the allocation of VMs in the generic version of
kvm_arch_alloc_vm(), the VM is tied to the current task/process.

Note, x86 already accounts its allocation.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/Y3aay2u2KQgiR0un@p183


[sean: reworded changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>