i386: hvf: header cleanup

Remove inclusions of system headers and avoid "pragma once".

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/target/i386/hvf/x86_decode.c b/target/i386/hvf/x86_decode.c
index 623c051..2a42a67 100644
--- a/target/i386/hvf/x86_decode.c
+++ b/target/i386/hvf/x86_decode.c
@@ -18,6 +18,7 @@
 
 #include "qemu/osdep.h"
 
+#include "qemu-common.h"
 #include "x86_decode.h"
 #include "string.h"
 #include "vmx.h"