vboot: remove OPROM-related code

As of CL:1605641, vboot2 code should be used for setting and
checking display init state.  Remove all vboot1 OPROM-related
code, and use the vboot2 display init code which has already
been added in previous commits.

coreboot should not be reading vboot NVRAM flags directly.
Remove the function vboot_wants_oprom(), and instead rely on
display_init_required(), which uses the
VBOOT_WD_FLAG_DISPLAY_INIT value stored in
vboot_working_data.flags, initialized during verstage.
Note that this means in the case of CONFIG_VBOOT=y, the return
value of display_init_required() can only be trusted after
verstage has been executed.  This should not be a problem
assuming that all display initialization occurs in ramstage.

BUG=b:124141368, b:124192753, chromium:948529
TEST=Build locally
TEST=make clean && make test-abuild
BRANCH=none

Change-Id: Ic8f9dc5a3c7f1546a8fed82bde02be4d04568f8d
Signed-off-by: Joel Kitching <kitching@google.com>
Cq-Depend: chromium:1605641, chromium:1605525
Reviewed-on: https://review.coreboot.org/c/coreboot/+/32723
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/soc/intel/broadwell/igd.c b/src/soc/intel/broadwell/igd.c
index 319549d..b9b4281 100644
--- a/src/soc/intel/broadwell/igd.c
+++ b/src/soc/intel/broadwell/igd.c
@@ -513,7 +513,7 @@
 	/* Wait for any configured pre-graphics delay */
 	if (!acpi_is_wakeup_s3()) {
 #if CONFIG(CHROMEOS)
-		if (display_init_required() || vboot_wants_oprom())
+		if (display_init_required())
 			mdelay(CONFIG_PRE_GRAPHICS_DELAY);
 #else
 		mdelay(CONFIG_PRE_GRAPHICS_DELAY);