gdb: Add LoongArch process record/replay support in NEWS and doc

At present, process record/replay and reverse debugging has been
implemented on LoongArch. Update the NEWS and doc to record this
new change.

Signed-off-by: Hui Li <lihui@loongson.cn>
Reviewed-By: Eli Zaretskii <eliz@gnu.org>
Approved-By: Tom Tromey <tom@tromey.com>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>