reboot: allow opting-in to fastbootd

Change-Id: Iaf5eb813e848ef05b1b455ebfe3643f4a8b4f80d
diff --git a/init/reboot.cpp b/init/reboot.cpp
index 1a26c4d..a9c1e36 100644
--- a/init/reboot.cpp
+++ b/init/reboot.cpp
@@ -1057,7 +1057,8 @@
             // adb reboot fastboot should boot into bootloader for devices not
             // supporting logical partitions.
             if (reboot_target == "fastboot" &&
-                !android::base::GetBoolProperty("ro.boot.dynamic_partitions", false)) {
+                !android::base::GetBoolProperty("ro.boot.dynamic_partitions", false) &&
+                !android::base::GetBoolProperty("ro.fastbootd.available", false)) {
                 reboot_target = "bootloader";
             }
             // When rebooting to the bootloader notify the bootloader writing