hw/riscv/virt.c: change 'aclint' TCG check

The 'aclint' property is being conditioned with tcg acceleration in
virt_machine_class_init(). But acceleration code starts later than the
class init of the board, meaning that tcg_enabled() will be always be
false during class_init(), and the option is never being declared even
when declaring TCG accel:

$ ./build/qemu-system-riscv64 -M virt,accel=tcg,aclint=on
qemu-system-riscv64: Property 'virt-machine.aclint' not found

Fix it by moving the check from class_init() to machine_init(). Tune the
description to mention that the option is TCG only.

Cc: Philippe Mathieu-Daudé <philmd@linaro.org>
Fixes: c0716c8 ("hw/riscv/virt: Restrict ACLINT to TCG")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1823
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20230811160224.440697-2-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

hw/riscv/virt.c

@@ -1350,6 +1350,11 @@ static void virt_machine_init(MachineState *machine)
         exit(1);
     }
 
+    if (!tcg_enabled() && s->have_aclint) {
+        error_report("'aclint' is only available with TCG acceleration");
+        exit(1);
+    }
+
     /* Initialize sockets */
     mmio_irqchip = virtio_irqchip = pcie_irqchip = NULL;
     for (i = 0; i < socket_count; i++) {
@@ -1683,13 +1688,14 @@ static void virt_machine_class_init(ObjectClass *oc, void *data)
     machine_class_allow_dynamic_sysbus_dev(mc, TYPE_TPM_TIS_SYSBUS);
 #endif
 
-    if (tcg_enabled()) {
-        object_class_property_add_bool(oc, "aclint", virt_get_aclint,
-                                       virt_set_aclint);
-        object_class_property_set_description(oc, "aclint",
-                                              "Set on/off to enable/disable "
-                                              "emulating ACLINT devices");
-    }
+
+    object_class_property_add_bool(oc, "aclint", virt_get_aclint,
+                                   virt_set_aclint);
+    object_class_property_set_description(oc, "aclint",
+                                          "(TCG only) Set on/off to "
+                                          "enable/disable emulating "
+                                          "ACLINT devices");
+
     object_class_property_add_str(oc, "aia", virt_get_aia,
                                   virt_set_aia);
     object_class_property_set_description(oc, "aia",