console_countdown: add possibility to abort countdown by external commands ...

This patch makes it possible to abort a console countdown by an external
command, for example when fastboot is used. This requires additional
modifications in the external commands, a call to "console_countdown_abort()"
has to be inserted.

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

timeout: factor out wait-for-key-press loop into separate file ...

This patch factors out the wait-for-key-press loop from the shell command
"timeout" into a sparate file, so that it can be used from C, too.

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>