x86: Build vga video code only if CONFIG_VIDEO_VGA is defined

When running from coreboot we don't want this code, so make it
optional.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index 2a3e8f0..0a52cc8 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -32,7 +32,7 @@
 SOBJS-y	+= realmode_switch.o
 
 COBJS-$(CONFIG_SYS_PC_BIOS)	+= bios_setup.o
-COBJS-$(CONFIG_VIDEO)	+= video_bios.o
+COBJS-$(CONFIG_VIDEO_VGA)	+= video_bios.o
 endif
 
 COBJS-y	+= board.o
@@ -50,7 +50,7 @@
 COBJS-y += physmem.o
 COBJS-y	+= string.o
 COBJS-$(CONFIG_SYS_X86_ISR_TIMER)	+= timer.o
-COBJS-$(CONFIG_VIDEO)	+= video.o
+COBJS-$(CONFIG_VIDEO_VGA)	+= video.o
 COBJS-$(CONFIG_CMD_ZBOOT)	+= zimage.o
 
 SRCS	:= $(SOBJS-y:.o=.S) $(COBJS-y:.o=.c)