Input: soc_button_array - convert to platform bus

ACPI device enumeration mechanism changed a lot since 3.16-rc1.
ACPI device objects with _HID will be enumerated to platform bus by default.
For the existing PNP drivers that probe the PNPACPI devices, the device ids
are listed explicitly in drivers/acpi/acpi_pnp.c.
But ACPI folks will continue their effort on shrinking this id list by
converting the PNP drivers to platform drivers, for the devices that don't
belong to PNP bus in nature.

Signed-off-by: Jin Yao <yao.jin@intel.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>