LoongArch: Make the CPUCFG&CSR ops simple aliases of compiler built-ins

In addition to less visual clutter, this also makes Clang happy
regarding the const-ness of arguments. In the original approach, all
Clang gets to see is the incoming arguments whose const-ness cannot be
proven without first being inlined; so Clang errors out here while GCC
is fine.

While at it, tweak several printk format strings because the return type
of csr_read64 becomes effectively unsigned long, instead of unsigned
long long.

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