f2fs: show the CP_PAUSE reason in checkpoint traces

Remove the duplicate CP_UMOUNT enum and add the new CP_PAUSE
enum to show the checkpoint reason in the trace prints.

Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>