x86: qemu: Add MP initialization

Add a cpu1 node to the device tree and enable the MP initialization
on QEMU targets (i440fx and q35).

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>

arch/x86/dts/qemu-x86_i440fx.dts

@@ -34,6 +34,13 @@
 			reg = <0>;
 			intel,apic-id = <0>;
 		};
+
+		cpu@1 {
+			device_type = "cpu";
+			compatible = "cpu-x86";
+			reg = <1>;
+			intel,apic-id = <1>;
+		};
 	};
 
 	pci {

arch/x86/dts/qemu-x86_q35.dts

@@ -45,6 +45,13 @@
 			reg = <0>;
 			intel,apic-id = <0>;
 		};
+
+		cpu@1 {
+			device_type = "cpu";
+			compatible = "cpu-x86";
+			reg = <1>;
+			intel,apic-id = <1>;
+		};
 	};
 
 	pci {

configs/qemu-x86_defconfig

 CONFIG_X86=y
 CONFIG_DEFAULT_DEVICE_TREE="qemu-x86_i440fx"
+CONFIG_SMP=y
+CONFIG_MAX_CPUS=2
 CONFIG_GENERATE_PIRQ_TABLE=y
 CONFIG_GENERATE_MP_TABLE=y
 CONFIG_CMD_CPU=y

doc/README.x86

@@ -281,6 +281,11 @@ QEMU emulates a graphic card which U-Boot supports. Removing '-nographic' will
 show QEMU's VGA console window. Note this will disable QEMU's serial output.
 If you want to check both consoles, use '-serial stdio'.
 
+Multicore is also supported by QEMU via '-smp n' where n is the number of cores
+to instantiate. Currently the default U-Boot built for QEMU supports 2 cores.
+In order to support more cores, you need add additional cpu nodes in the device
+tree and change CONFIG_MAX_CPUS accordingly.
+
 CPU Microcode
 -------------
 Modern CPUs usually require a special bit stream called microcode [8] to be