ideapad_laptop: convert ideapad device/driver to platform bus

This patch does two things,
 1. enumerate the ideapad device node to platform bus.
 2. convert the current driver from ACPI bus to platform bus.

Note, with this patch, the platform device node created by ACPI,
with the name VPC2004:00, is used as the parent device of
the input, backlight, rfkill sysfs class device.
Plus the ideapad_platform private sysfs attributes,
i.e. camera_power and fan_mode, are also moved to the new
platform device node.

The previous platform device node "ideapad" is removed.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
CC: Matthew Garrett <matthew.garrett@nebula.com>
CC: Ike Panhc <ike.pan@canonical.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>