mfd: twl-core: re-group the twl_mapping table for easier reading

Group the twl_mapping table in 5 lines chunks so it is more easier to find
the row we are looking for (if we need to).

Acked-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>