AP_Bootloader: cope with RAM0_START not matching between bl and periph

this allows us to stay in bootloader based solely on RTC_BOOT_CANBL
without the RAM0 area matching between bootloader and periph fw

fixes an issue with current bootloaders where the old bl may not match
current RAM0 value

Tools/AP_Bootloader/AP_Bootloader.cpp

@@ -136,8 +136,9 @@ int main(void)
     }
 #endif  // AP_CHECK_FIRMWARE_ENABLED
 #ifndef BOOTLOADER_DEV_LIST
-    else if (timeout != 0) {
-        // fast boot for good firmware
+    else if (timeout == HAL_BOOTLOADER_TIMEOUT) {
+        // fast boot for good firmware if we haven't been told to stay
+        // in bootloader
         try_boot = true;
         timeout = 1000;
     }