ext4: get rid of super block and sbi from handle_mount_ops()

At the parsing phase of mount in the new mount api sb will not be
available. We've already removed some uses of sb and sbi, but now we
need to get rid of the rest of it.

Use ext4_fs_context to store all of the configuration specification so
that it can be later applied to the super block and sbi.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Link: https://lore.kernel.org/r/20211027141857.33657-9-lczerner@redhat.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>