gdb: NEWS: Move LoongArch gdbserver to the correct section

commit e5ab6af52d38 ("gdbserver: Add LoongArch/Linux support")
was merged into the master since GDB 12, so we should put the
news in the "Changes since GDB 12" section.

Thanks Tom Tromey for your correction [1], sorry for that.

[1] https://sourceware.org/pipermail/gdb-patches/2022-June/190122.html

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>