fbdev: ignore VESA modes if framebuffer is disabled

If the option vga=<VESA graphics mode> is added to the boot parameter, it will
activate graphics mode, but without any framebuffer support, the user is left
with an unusable display.

Change the behavior such that the user is instead prompted for another mode
(ala vga=ask).

NOTE: People can always use vbetool to set a graphics mode if this is really
desired, but the number of people doing this approaches zero.

Signed-off-by: Antonino Daplas <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>