qemu: packaging target {x86_64,arm}-softmmu and friends

At the moment, only build these softmmu emulators for x86_64 and sunxi
target.  The decision was made for the following reasons

 - It seems that interests of virtualization with qemu are mostly from
   x86, and ARM recently.
 - x86, sunxi boards/boxes capable of running qemu with accel=kvm are more
   widely available
 - Not all host, target combinations of qemu works, or even compiles
 - Extra maintenance work and server resources

Test results are as the following

 - Nested vmx works: lede-qemu-x86_64-kvm on lede-qemu-x86_64-kvm
 - KVM on Cubieboard2 works
 - tcg with malta works: lede-qemu-malta-tcg on lede-qemu-malta-tcg.
   But it's too slow to be useful thus not included in this version
 - mips64 host does not compile

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

utils/qemu/patches/0005-pixman-arm-neon-assembler-fix.patch

@@ -0,0 +1,17 @@
+--- a/pixman/pixman/pixman-private.h.orig	2016-11-22 22:10:33.574769654 +0800
++++ b/pixman/pixman/pixman-private.h	2016-11-22 22:10:47.638774056 +0800
+@@ -1,5 +1,3 @@
+-#include <float.h>
+-
+ #ifndef PIXMAN_PRIVATE_H
+ #define PIXMAN_PRIVATE_H
+ 
+@@ -17,6 +15,8 @@
+ 
+ #ifndef __ASSEMBLER__
+ 
++#include <float.h>
++
+ #ifndef PACKAGE
+ #  error config.h must be included before pixman-private.h
+ #endif