LoongArch: Fix format of CSR lines during show_regs()

Use uppercase CSR names throughout for consistency with the manual
wording, and right-align the keys. The "CSR" part is inferrable from
context, hence dropped for more horizontal space.

Signed-off-by: WANG Xuerui <git@xen0n.name>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>