ext4: Change handle_mount_opt() to use fs_parameter

Use the new mount option specifications to parse the options in
handle_mount_opt(). However we're still using the old API to get the
options string.

Signed-off-by: Lukas Czerner <[email protected]>
Reviewed-by: Carlos Maiolino <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Theodore Ts'o <[email protected]>

Author: Lukas Czerner