mfd: twl: Convert module id definitions to enums

Use enum list for the module definitions (TWL4030_MODULE_*) which will ease
up future work with the IDs.
At the same time group the IDs in block of five so it is easier to find the
ID we are looking for (to count the number they stand for).

At the same time define TWL_MODULE_LED so client drivers can switch to use
it as soon as it is possible.

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>