regulator: MAX8997/8966 support

regulator: MAX8997/8966 support

This patch supports PMIC/Regulator part of MAX8997/MAX8966 MFD.
In this initial release, selecting voltages or current-limit
and switching on/off the regulators are supported.

Controlling voltages for DVS with GPIOs is not implemented fully
and requires more considerations: it controls multiple bucks (selection
of 1, 2, and 5) at the same time with SET1~3 gpios. Thus, when DVS-GPIO
is activated, we lose the ability to control the voltage of a single
buck regulator independently; i.e., contolling a buck affects other two
bucks. Therefore, using the conventional regulator framework directly
might be problematic. However, in this driver, we try to choose
a setting without such side effect of affecting other regulators and
then try to choose a setting with the minimum side effect (the sum of
voltage changes in other regulators).

On the other hand, controlling all the three bucks simultenously based
on the voltage set table may help build cpufreq and similar system
more robust; i.e., all the three voltages are consistent every time
without glitches during transition.

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>