configs/qemu: enable SMP for x86 & x86_64

This is the 21st century, so enable SMP for them.

[Peter: add note to readme.txt about how emulate a SMP system in QEMU]
Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

board/qemu/x86/linux-4.3.config

@@ -1,4 +1,5 @@
 CONFIG_SYSVIPC=y
+CONFIG_SMP=y
 CONFIG_NET=y
 CONFIG_PACKET=y
 CONFIG_UNIX=y

board/qemu/x86/readme.txt

@@ -2,6 +2,8 @@ Run the emulation with:
 
   qemu-system-i386 -M pc -kernel output/images/bzImage -drive file=output/images/rootfs.ext2,if=ide,format=raw -append root=/dev/sda -net nic,model=rtl8139 -net user
 
+Optionally add -smp N to emulate a SMP system with N CPUs.
+
 The login prompt will appear in the graphical window.
 
 Tested with QEMU 2.3.0

board/qemu/x86_64/linux-4.3.config

@@ -1,4 +1,5 @@
 CONFIG_SYSVIPC=y
+CONFIG_SMP=y
 CONFIG_NET=y
 CONFIG_PACKET=y
 CONFIG_UNIX=y

board/qemu/x86_64/readme.txt

@@ -2,6 +2,8 @@ Run the emulation with:
 
   qemu-system-x86_64 -M pc -kernel output/images/bzImage -drive file=output/images/rootfs.ext2,if=ide,format=raw -append root=/dev/sda -net nic,model=rtl8139 -net user
 
+Optionally add -smp N to emulate a SMP system with N CPUs.
+
 The login prompt will appear in the graphical window.
 
 Tested with QEMU 2.3.0