mfd: twl-core: Add initial DT support for twl4030/twl6030

mfd: twl-core: Add initial DT support for twl4030/twl6030

Add initial device-tree support for twl familly chips.
The current version is missing the regulator entries due
to the lack of DT regulator bindings for the moment.
Only the simple sub-modules that do not depend on
platform_data information can be initialized properly.

Add irqdomain support.

Add documentation for the Texas Instruments TWL Integrated Chip.

Signed-off-by: Benoit Cousson <[email protected]>
Cc: Balaji T K <[email protected]>
Cc: Graeme Gregory <[email protected]>
Signed-off-by: Samuel Ortiz <[email protected]>
Acked-by: Rob Herring <[email protected]>
[[email protected]: Fix IRQ_DOMAIN dependency in kconfig]
Cc: Grant Likely <[email protected]>