Adds new syscalls on ARM and AArch64 upto kernel 5.5.
Also removes conditional compilation for the syscalls which were previously defined only on some architectures.
The updated #defines are copied from linux headers. In some cases, the existing version in DR was different, so the diff is bigger. But I verified that all of the previous ones are still present; one of the old ones had to be added separately (pointed out using a comment).
Split from #5143.
Issue: #5131 (closed)