sdl: Consistently avoid grabbing input for text consoles

sdl: Consistently avoid grabbing input for text consoles

There were some preexisting bits that released the input when switching
to text console. This patch spreads this logic consistently and also
avoids grabbing the input while a text console is active.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>