Sync events are sent by sparse_keymap_report_entry for normal KEY_*
events, and are generated by several drivers after generating
SW_* events, so sparse_keymap_report_entry should do the same.

Without the sync, events are accumulated in the kernel.

Currently, no driver uses sparse-keymap for SW_* events, but
it is required for the intel-vbtn platform driver to generate
SW_TABLET_MODE events.
Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>