ACPI: thinkpad-acpi: revert new 2.6.23 CONFIG_THINKPAD_ACPI_INPUT_ENABLED option

ACPI: thinkpad-acpi: revert new 2.6.23 CONFIG_THINKPAD_ACPI_INPUT_ENABLED option

Revert new 2.6.23 CONFIG_THINKPAD_ACPI_INPUT_ENABLED Kconfig option because
it would create a legacy we don't want to support.

CONFIG_THINKPAD_ACPI_INPUT_ENABLED was added to try to fix an issue that is
now moot with the addition of the netlink ACPI event report interface to
the ACPI core.

Now that ACPI core can send events over netlink, we can use a different
strategy to keep backwards compatibility with older userspace, without the
need for the CONFIG_THINKPAD_ACPI_INPUT_ENABLED games.  And it arrived
before CONFIG_THINKPAD_ACPI_INPUT_ENABLED made it to a stable mainline
kernel, even, which is Good.

This patch is in sync with some changes to thinkpad-acpi backports, that
will keep things sane for userspace across different combinations of kernel
versions, thinkpad-acpi backports (or the lack thereof), and userspace
capabilities:

Unless a module parameter is used, thinkpad-acpi will now behave in such a
way that it will work well (by default) with userspace that still uses only
the old ACPI procfs event interface and doesn't care for thinkpad-acpi
input devices.

It will also always work well with userspace that has been updated to use
both the thinkpad-acpi input devices, and ACPI core netlink event
interface, regardless of any module parameter.

The module parameter was added to allow thinkpad-acpi to work with
userspace that has been partially updated to use thinkpad-acpi input
devices, but not the new ACPI core netlink event interface.  To use this
mode of hot key reporting, one has to specify the hotkey_report_mode=2
module parameter.

The thinkpad-acpi driver exports the value of hotkey_report_mode through
sysfs, as well.  thinkpad-acpi backports to older kernels, that do not
support the new ACPI core netlink interface, have code to allow userspace
to switch hotkey_report_mode at runtime through sysfs.  This capability
will not be provided in mainline thinkpad-acpi as it is not needed there.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Michael S. Tsirkin <mst@dev.mellanox.co.il>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Richard Hughes <hughsient@gmail.com>
Signed-off-by: Len Brown <len.brown@intel.com>