security/vboot: make vboot starts in bootblock depend on c env

coreboot on skylake originally did ship with romcc bootblock and
verstage running after it. However, that configuration makes boot
flows very complicated. No platform in the current code base uses
this combination. Make VBOOT_STARTS_IN_BOOTBLOCK depend on
C_ENVIRONMENT_BOOTBLOCK.

BUG=b:78656686

Change-Id: Ia9446f209521f71c91b83d579b9e2d89744292bc
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/25984
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-by: Justin TerAvest <teravest@chromium.org>
Reviewed-by: Hannah Williams <hannah.williams@intel.com>
diff --git a/src/security/vboot/Kconfig b/src/security/vboot/Kconfig
index 8d8e120..0139d25 100644
--- a/src/security/vboot/Kconfig
+++ b/src/security/vboot/Kconfig
@@ -67,6 +67,7 @@
 config VBOOT_STARTS_IN_BOOTBLOCK
 	bool
 	default n
+	depends on C_ENVIRONMENT_BOOTBLOCK
 	help
 	  Firmware verification happens during the end of or right after the
 	  bootblock. This implies that a static VBOOT2_WORK() buffer must be