f2fs: Add fs parameter specifications for mount options

Use an array of `fs_parameter_spec` called f2fs_param_specs to
hold the mount option specifications for the new mount api.

Add constant_table structures for several options to facilitate
parsing.

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