[gdb/syscalls] Add syscalls {set,get,list,remove}xattrat

[gdb/syscalls] Add syscalls {set,get,list,remove}xattrat

In commit 58776901074 ("[gdb/syscalls] Update to linux v6.11") I updated to
linux v6.11, but a recent submission for loongarch [1] used a current trunk
version, so it makes sense to do this as well elsewhere.

Using linux current trunk with update-linux-from-src.sh gets us 4 more
syscalls:
- setxattrat
- getxattrat
- listxattrat
- removexattrat

Tested on x86_64-linux.

[1] https://sourceware.org/pipermail/gdb-patches/2024-November/213613.html