Unblank display when shutting down/rebooting from act dead or user mode

Previously display was blanked when shutting down from act dead. As there
is now shutdown animation also for act dead, that is no longer desirable.

Unblanking the display makes the animation visible even if the shutdown
or reboot happened from display off state without user interaction.
Keep frame buffer device opened to keep display from powering off

When mce starts up, it will keep the fbdev open until actdead or
user mode is reached. This should keep the display powered on and
not lose content during bootup.

When shutdown is initiated (and not canceled), mce opens fbdev and
keeps it open for a while even after mce exits to allow shutdown
animation to stay visible.

[mce] Keep frame buffer device opened to keep display from powering off. Fixes JB#14341
Merge pull request #185 from spiiroin/delay_shutdown_blanking

Delay display blanking during shutdown