objtool/LoongArch: Mark types based on break immediate code

If the break immediate code is 0, it should mark the type as
INSN_TRAP. If the break immediate code is 1, it should mark the
type as INSN_BUG.

While at it, format the code style and add the code comment for nop.

Cc: stable@vger.kernel.org
Suggested-by: WANG Rui <wangrui@loongson.cn>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>