common/lcd_console: move single static variables into common (static) structure

For coming implementation of lcd_console rotation, we will need some more
variables for holding information about framebuffer size, rotation, ...

For better readability we catch all them into a common structure.

Signed-off-by: Hannes Petermaier <hannes.petermaier@br-automation.com>
Signed-off-by: Hannes Petermaier <oe5hpm@oevsv.at>
Acked-by: Nikita Kiryanov <nikita@compulab.co.il>