qemu-system-riscv64 Property 'virt-machine.aclint' not found
Description of problem:

Steps to reproduce:
1.  run ./qemu-system-riscv64 -M virt,aclint=on
2. command output: 
```
qemu-system-riscv64: Property 'virt-machine.aclint' not found
```
Additional information:
The aclint property is registered in the virt_machine_class_init function and depends on the condition tcg_enabled(), but the initialization of tcg_enabled() is later than the call of virt_machine_class_init. This caused the aclint property to never be registered.