Move <machine/endian.h> somewhere more private.

Bug: http://b/28519060
Change-Id: I1c7811f95f46c65d4152bcf509b6e048c45bc28b
diff --git a/libc/upstream-freebsd/android/include/machine/endian.h b/libc/upstream-freebsd/android/include/machine/endian.h
new file mode 100644
index 0000000..2dc4d83
--- /dev/null
+++ b/libc/upstream-freebsd/android/include/machine/endian.h
@@ -0,0 +1 @@
+#include <endian.h>