LoongArch: Use str_yes_no() helper function for /proc/cpuinfo

Remove hard-coded strings by using the str_yes_no() helper function.

Similar to commit c4a0a4a45a45 ("MIPS: kernel: proc: Use str_yes_no()
helper function").

Co-developed-by: Wentao Guan <guanwentao@uniontech.com>
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
Signed-off-by: Yuli Wang <wangyuli@uniontech.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>