framebuffer: disable vgacon on microblaze arch

Fix an allmodconfig link failer on microblaze:
  drivers/built-in.o: In function `vgacon_save_screen':
  drivers/video/console/.tmp_vgacon.o:(.text+0x8fc10):
    undefined reference to `screen_info'

Disable vgacon on microblaze because the symbol
  struct screen_info screen_info;
is not defined for the microblaze arch.

Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/video/console/Kconfig

@@ -9,7 +9,7 @@ config VGA_CONSOLE
 	depends on !4xx && !8xx && !SPARC && !M68K && !PARISC && !FRV && \
 		!SUPERH && !BLACKFIN && !AVR32 && !MN10300 && !CRIS && \
 		(!ARM || ARCH_FOOTBRIDGE || ARCH_INTEGRATOR || ARCH_NETWINDER) && \
-		!ARM64
+		!ARM64 && !MICROBLAZE
 	default y
 	help
 	  Saying Y here will allow you to use Linux in text mode through a