mfd: add base support for Dialog DA9030/DA9034 PMICs

DA9030 (a.k.a ARAVA) and DA9034 (a.k.a MICCO) are PMICs designed by
Dialog Semiconductor, usually found on PXA-based platforms. These
PMICs are I2C-based, multi-function devices, usually with LEDs, PWMs
for backlight, BUCKs and LDOs, ADCs and touchscreen controller (on
DA9034).

This is the base support for the I2C operations, event registration
and handling, sub-devices management.

Signed-off-by: Mike Rapoport <mike@compulab.co.il>
Signed-off-by: Eric Miao <eric.miao@marvell.com>
Signed-off-by: Liam Girdwood <lrg@kernel.org>
Signed-off-by: Samuel Ortiz <sameo@openedhand.com>