fbdev: link vgastate.o using Kconfig

Instead of directly linking vgastate.o by individual drivers, create a Kconfig
option VGASTATE which can be 'SELECT'ed by individual drivers instead.

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