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/include/lp_vboot.h

@@ -7,4 +7,13 @@
 
 struct vb2_context *vboot_get_context(void);
 
+/*
+ * Call vb2api_fail() with reason and subcode, save vboot data with vb2ex_commit_data()
+ * and reboot with vboot_reboot().
+ */
+void vboot_fail_and_reboot(struct vb2_context *ctx, uint8_t reason, uint8_t subcode);
+
+/* Returns non-zero if recovery mode is enabled. */
+int vboot_recovery_mode_enabled(void);
+
 #endif /* _LP_VBOOT_H_ */