Fix compilation due to missing headers on OpenBSD/powerpc

When the code for detecting the number of CPUs present was moved
the headers necessary to compile the AltiVec detection code on
OpenBSD/powerpc was mistakenly removed so this puts the headers
back as appropriate.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
(cherry picked from commit 6f8c945b)

src/misc/cpu.c

@@ -47,6 +47,12 @@
 #include <sys/sysctl.h>
 #endif
 
+#if defined(__OpenBSD__) && defined(__powerpc__)
+#include <sys/param.h>
+#include <sys/sysctl.h>
+#include <machine/cpu.h>
+#endif
+
 #include "libvlc.h"
 
 static uint32_t cpu_flags;