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>

include/fastboot.h

@@ -52,6 +52,15 @@ enum fastboot_reboot_reason {
 	FASTBOOT_REBOOT_REASONS_COUNT
 };
 
+/**
+ * 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".
  *