hw/riscv: sifive_u: Use SIFIVE_U_CPU for mc->default_cpu_type

SIFIVE_U_CPU is conditionally set to SIFIVE_U34 or SIFIVE_U54, hence
there is no need to use #idef to set the mc->default_cpu_type.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20210109143637.29645-1-bmeng.cn@gmail.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

hw/riscv/sifive_u.c

@@ -628,11 +628,7 @@ static void sifive_u_machine_class_init(ObjectClass *oc, void *data)
     mc->init = sifive_u_machine_init;
     mc->max_cpus = SIFIVE_U_MANAGEMENT_CPU_COUNT + SIFIVE_U_COMPUTE_CPU_COUNT;
     mc->min_cpus = SIFIVE_U_MANAGEMENT_CPU_COUNT + 1;
-#if defined(TARGET_RISCV32)
-    mc->default_cpu_type = TYPE_RISCV_CPU_SIFIVE_U34;
-#elif defined(TARGET_RISCV64)
-    mc->default_cpu_type = TYPE_RISCV_CPU_SIFIVE_U54;
-#endif
+    mc->default_cpu_type = SIFIVE_U_CPU;
     mc->default_cpus = mc->min_cpus;
 
     object_class_property_add_bool(oc, "start-in-flash",