Kconfig: Move and clean up CONFIG_VGA

Change-Id: I6e710b95cade0ea68f787f33c0070613d64b6da6
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/19743
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/drivers/pc80/vga/Kconfig

@@ -0,0 +1,4 @@
+config VGA
+	bool
+	help
+	  Include legacy VGA support code.