refactor vesa mode setting code and bootsplash code

refactor vesa mode setting code and bootsplash code

- adds possibility to set a vesa mode without showing a bootsplash
- make bootsplash / mode setting code available in real mode.

Change-Id: I0045c9d75757657f4ce531889593102ea1e39ce5
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/256
Tested-by: build bot (Jenkins)
Reviewed-by: Marc Jones <marcj303@gmail.com>