mfd: twl-core: Clean up module id lookup and definitions

Use enums for all module definitions:
twl_module_ids for common functionality among twl4030/twl6030
twl4030_module_ids for twl4030 specific ids
twl6030_module_ids for twl6030 specific ids

In this way the list can be managed easier when new functionality going to
be implemented.

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