platform/x86: thinkpad_acpi: Add sysfs control for TrackPoint double-tap

platform/x86: thinkpad_acpi: Add sysfs control for TrackPoint double-tap

Add a sysfs attribute to enable or disable TrackPoint double-tap hotkey
events at the kernel level.

The TrackPoint firmware enables double-tap support automatically. This
interface allows userspace to control whether double-tap events are
forwarded to userspace.

The attribute is available at:

  /sys/devices/platform/thinkpad_acpi/doubletap_enable

  0 - Disable double-tap hotkey events
  1 - Enable double-tap hotkey events (default)

Filtering is implemented by suppressing ACPI hotkey delivery without
injecting synthetic input events.

Signed-off-by: Vishnu Sankar <vishnuocv@gmail.com>
Suggested-by: Mark Pearson <mpearson-lenovo@squebb.ca>
Link: https://patch.msgid.link/20260311143144.482145-3-vishnuocv@gmail.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>