Disable DFU_BTN check

The BTT SKR 1.3 puts the E0 enable pin on P2.12, which happens to be the "play" pin on the original smoothieboard. This release disables that check to keep stepper drivers from interfering with the boot sequence. Unlike the bootloader that ships with the SKR 1.3, this bootloader makes it possible to enter DFU mode via the application.

Note that betterBootloader.bin can be used to update the bootloader by using the sd card:

• Put betterBootloader.bin on your sd card and rename it firmware.bin
• Insert the sd card into the SKR 1.3
• Power on the SKR 1.3 (or reset if already powered on)
• Wait 10 seconds, then reset
• The new bootloader should be flashed along with Klipper. You can now flash using USB/DFU or using the sd card.

The IAP firmware used to flash the bootloader via sdcard is courtesy of @mattthebaker and can be found here.

The FABULOUS name "betterBootloader.bin" is courtesy of @timmit99. Please heap praise on him accordingly.

Disclaimer: This software is distributed as-is with no guarantees. While the firmware works fine in our testing, neither myself nor @mattthebaker are responsible for any malfunction that may occur as a result of flashing it.