bootmode: add display_init_required()

Some of the Chrome OS boards were directly calling vboot
called in some form after contorting around #ifdef preprocessor
macros. The reasoning is that Chrome OS doesn't always do display
initialization during startup. It's runtime dependent. While
this is a requirement that doesn't mean vboot functions should be
sprinkled around in the mainboard and chipset code. Instead provide
one function, display_init_required(), that provides the policy
for determining display initialization action. For Chrome OS
devices this function honors vboot_skip_display_init() and all
other configurations default to initializing display.

Change-Id: I403213e22c0e621e148773597a550addfbaf3f7e
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/11490
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

src/mainboard/google/rush_ryu/mainboard.c

@@ -19,6 +19,7 @@
 
 #include <arch/mmu.h>
 #include <boardid.h>
+#include <bootmode.h>
 #include <boot/coreboot_tables.h>
 #include <cbmem.h>
 #include <delay.h>
@@ -281,7 +282,7 @@ static void mainboard_init(device_t dev)
 	soc_configure_pads(lcd_gpio_padcfgs, ARRAY_SIZE(lcd_gpio_padcfgs));
 
 	/* if panel needs to bringup */
-	if (!vboot_skip_display_init())
+	if (display_init_required())
 		configure_display_blocks();
 }