input: cpcap-pwrbutton: New driver

Motorola CPCAP is a PMIC found in multiple smartphones.
This driver adds support for the power/on button and has
been tested in Droid 4.

Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>