security/vboot: Use persistent context to read GBB flags

With the persistent vboot context coreboot no longer needs to read GBB
flags from flash itself -- it can just ask vboot for the cached result.
This patch removes the existing GBB code and provides gbb_is_flag_set()
(with a slightly better namespaced name) as a static inline instead.

Change-Id: Ibc3ed0f3fbeb53d630925d47df4dc474b0ed07ee
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37261
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Joel Kitching <kitching@google.com>

src/security/vboot/misc.h

@@ -49,6 +49,17 @@ static inline int vboot_is_firmware_slot_a(const struct vb2_context *ctx)
 	return !(ctx->flags & VB2_CONTEXT_FW_SLOT_B);
 }
 
+/*
+ * Check if given flag is set in the flags field in GBB header.
+ * Return value:
+ * true: Flag is set.
+ * false: Flag is not set.
+ */
+static inline bool vboot_is_gbb_flag_set(enum vb2_gbb_flag flag)
+{
+	return !!(vb2api_gbb_get_flags(vboot_get_context()) & flag);
+}
+
 /*
  * Locates firmware as a region device. Returns 0 on success, -1 on failure.
  */