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/libpayload.h

@@ -414,6 +414,13 @@ void mouse_cursor_add_input_driver(struct mouse_cursor_input_driver *in);
  * @{
  */
 int exec(long addr, int argc, char **argv);
+
+/*
+ * reboot() handles reboot requests made by libpayload. It has weak implementation
+ * which should be overridden by payload.
+ */
+void __noreturn reboot(void);
+
 /** @} */
 
 /**