fastboot: Add default fastboot_set_reboot_flag implementation

Default implementation of fastboot_set_reboot_flag function that depends
on "bcb" commands could be used in general case if there are no need to
make any platform-specific implementation, otherwise it could be
disabled via Kconfig option FASTBOOT_USE_BCB_SET_REBOOT_FLAG.

Please note that FASTBOOT_USE_BCB_SET_REBOOT_FLAG is mutually exclusive
with some platforms which already have their own implementation of this
function.

Signed-off-by: Roman Kovalivskyi <roman.kovalivskyi@globallogic.com>
diff --git a/include/fastboot.h b/include/fastboot.h
index b86b508..8e9ee80 100644
--- a/include/fastboot.h
+++ b/include/fastboot.h
@@ -53,6 +53,15 @@
 };
 
 /**
+ * BCB boot commands
+ */
+static const char * const fastboot_boot_cmds[] = {
+	[FASTBOOT_REBOOT_REASON_BOOTLOADER] = "bootonce-bootloader",
+	[FASTBOOT_REBOOT_REASON_FASTBOOTD] = "boot-fastboot",
+	[FASTBOOT_REBOOT_REASON_RECOVERY] = "boot-recovery"
+};
+
+/**
  * fastboot_response() - Writes a response of the form "$tag$reason".
  *
  * @tag: The first part of the response