When global.autoboot_abort_key is set to ctrl-c then the user is
expected to press ctrl-c to get to the prompt. The user might press
ctrl-c before the init script runs the "timeout" command. In this
case the init script is aborted at arbitrary places which leads to
inconsistent results depending on the place it is aborted.

This patch introduces the global.console.ctrlc_allowed variable.
When this variable is set to false ctrl-c is ignored entirely.
The variable is set to false by default and changed to true in
the init script.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>