Input: touchscreen - broaden use-cases described in comments

Input: touchscreen - broaden use-cases described in comments

Now that the helper functions have been moved to drivers/input/ so
that all input devices may use them, the introductory comments can
be updated to remove any implication that the helper functions are
solely limited to touchscreens.

This patch also scrubs any remaining use of 'DT' since there isn't
any actual dependency on OF. A minor spelling error is resolved as
well ('setups' -> 'sets up').

Signed-off-by: Jeff LaBundy <jeff@labundy.com>
Link: https://lore.kernel.org/r/20210301234928.4298-3-jeff@labundy.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>