riscv: sifive_u: Set the minimum number of cpus to 2

It is not useful if we only have one management CPU.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
[Palmer: Set default CPUs to 2]
Reviewed-by: Palmer Dabbelt <palmer@sifive.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

include/hw/riscv/sifive_u.h

@@ -69,6 +69,8 @@ enum {
     SIFIVE_U_GEM_CLOCK_FREQ = 125000000
 };
 
+#define SIFIVE_U_MANAGEMENT_CPU_COUNT   1
+
 #define SIFIVE_U_PLIC_HART_CONFIG "MS"
 #define SIFIVE_U_PLIC_NUM_SOURCES 54
 #define SIFIVE_U_PLIC_NUM_PRIORITIES 7