f2fs: Add f2fs_fs_context to record the mount options

At the parsing phase of mouont in the new mount api, options
value will be recorded with the context, and then it will be
used in fill_super and other helpers.

Note that, this is a temporary status, we want remove the sb
and sbi usages in handle_mount_opt. So here the f2fs_fs_context
only records the mount options, it will be copied in sb/sbi in
later process. (At this point in the series, mount options are
temporarily not set during mount.)

Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
[sandeen: forward port, minor fixes and updates]
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
[hongbo: minor cleanup]
Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>