libpayload: Add vboot and reboot utility functions

Patch adds:
- vboot_fail_and_reboot() for vboot failures handling.
- reboot() weak implementation for payloads to implement, used
  by vboot_fail_and_reboot().
- vboot_recovery_mode_enabled() to check if recovery mode flag is set in
  vboot context. Implemented for future libcbfs implementation
  of VBOOT_CBFS_INTEGRATION in libpayload.

BUG=b:197114807
TEST=none

Change-Id: I53d1955573d54bc56d05f7780c18dcc8ac1fd399
Signed-off-by: Jakub Czapiga <jacz@semihalf.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/77725
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>

payloads/libpayload/libc/lp_vboot.c

@@ -26,3 +26,18 @@ struct vb2_context *vboot_get_context(void)
 
 	return ctx;
 }
+
+void vboot_fail_and_reboot(struct vb2_context *ctx, uint8_t reason, uint8_t subcode)
+{
+	if (reason)
+		vb2api_fail(ctx, reason, subcode);
+
+	printf("vboot: reboot requested (reason: %#x, subcode %#x)", reason, subcode);
+	vb2ex_commit_data(ctx);
+	reboot();
+}
+
+int vboot_recovery_mode_enabled(void)
+{
+	return !!(vboot_get_context()->flags & VB2_CONTEXT_RECOVERY_MODE);
+}