RISC-V: Enable CPU Hotplug in defconfigs

The CPU hotplug support has been tested on QEMU, Spike, and SiFive
Unleashed so let's enable it by default in RV32 and RV64 defconfigs.
Signed-off-by: Anup Patel <anup.patel@wdc.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/configs/defconfig

@@ -17,6 +17,7 @@ CONFIG_BPF_SYSCALL=y
 CONFIG_SOC_SIFIVE=y
 CONFIG_SOC_VIRT=y
 CONFIG_SMP=y
+CONFIG_HOTPLUG_CPU=y
 CONFIG_JUMP_LABEL=y
 CONFIG_MODULES=y
 CONFIG_MODULE_UNLOAD=y

arch/riscv/configs/rv32_defconfig

@@ -18,6 +18,7 @@ CONFIG_SOC_SIFIVE=y
 CONFIG_SOC_VIRT=y
 CONFIG_ARCH_RV32I=y
 CONFIG_SMP=y
+CONFIG_HOTPLUG_CPU=y
 CONFIG_JUMP_LABEL=y
 CONFIG_MODULES=y
 CONFIG_MODULE_UNLOAD=y