input: PCAP2 misc input driver

This is a driver for misc input events for the PCAP2 PMIC, it handles
the Power key and the Headphone button.

Signed-off-by: Daniel Ribeiro <drwyrm@gmail.com>
Signed-off-by: Ilya Petrov <ilya.muromec@gmail.com>
Signed-off-by: Antonio Ospite <ospite@studenti.unina.it>
Acked-by: Dmitry Torokhov <dtor@mail.ru>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>