Add -smp 4 to QEMU run command for multi-core simulation

Enable running the kernel on 4 simulated cores by passing the -smp 4
parameter to qemu-system-riscv32, facilitating SMP testing and
development.

Author: visitorckw

arch/riscv/build.mk

@@ -49,4 +49,4 @@ $(BUILD_KERNEL_DIR)/%.o: $(ARCH_DIR)/%.c | $(BUILD_DIR)
 
 run:
 	@$(call notice, Ready to launch Linmo kernel + application.)
-	$(Q)qemu-system-riscv32 -machine virt -nographic -bios none -kernel $(BUILD_DIR)/image.elf -nographic
+	$(Q)qemu-system-riscv32 -smp 4 -machine virt -nographic -bios none -kernel $(BUILD_DIR)/image.elf -nographic