The drivers don't really need to know which PMIC they're for, so
make a generic binding for them. This alleviates us from updating
the drivers every time a new PMIC comes out. It's still
recommended that we update the binding with new PMIC models and
always specify the specific model for the MPPs and gpios before
the generic compatible string in devicetree, but this at least
cuts down on adding more and more compatible strings to the
drivers until we actually need them.

Cc: <devicetree@vger.kernel.org>
Acked-by: "Ivan T. Ivanov" <iivanov.xz@gmail.com>
Reviewed-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>