alpha: VGA_HOSE depends on VGA_CONSOLE

arch/alpha/kernel/console.c:locate_and_init_vga uses vga_con, causing
build failures if VGA_CONSOLE was not set and MARVEL, TITAN, DP264, or
GENERIC alpha system types were set.

Reported-by: Raúl Porcel <armin76@gentoo.org>
Signed-off-by: Matt Turner <mattst88@gmail.com>