gdb: syscalls: Update LoongArch xml files

There are some new syscalls in the latest upstream Linux kernel [1][2][3],
update the xml files for LoongArch to reflect the reality.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7697a0fe0154
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ff388fe5c481
[3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6140be90ec70

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Approved-By: Tom de Vries <tdevries@suse.de>