docs/LoongArch: Update links of LoongArch ISA Vol1 and ELF psABI

The current links of LoongArch ISA Vol1 and ELF psABI are invalid,
the latest versions are 1.02 and 2.00 respectively, let us update
the links.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Link: https://lore.kernel.org/r/1669892345-7763-2-git-send-email-yangtiezhu@loongson.cn


Signed-off-by: Jonathan Corbet <corbet@lwn.net>