Correct MCU/Board relationship

https://www.pjrc.com/teensy/jump_to_bootloader.html (2021/Dec)

Each board has a different beginning address for the bootloader.

Original bootloaders for Teensy 2 comes with a proprietary 512 Byte HID
bootloader called halfkey.  So the address needs to be adjusted for
bigger LUFA bootloaders.  For free 512 Byte bootloaders for ATMEGA32U4,
see:

  * https://github.com/volium/nanoBoot    (original)
  * https://github.com/osamuaoki/nanoBoot (LED mod, me)
  * https://github.com/sigprof/nanoBoot   (Mac mod)

(I have no information on other original bootloaders)

PJRC site lists:

Model        Chip          Jump Address   Estimated max bootloader size
                           (byte address)

Teensy   1.0 AT90USB162       0x3E00      ( 512 Byte max)
Teensy++ 1.0 AT90USB646       0xFC00      (2048 Byte max)

Teensy   2.0 ATMEGA32U4       0x7E00      ( 512 Byte max)
Teensy++ 2.0 AT90USB1286     0x1FC00      (2048 Byte max)

LED pins are always at D6 but its polarity changed from Teensy/Teensy++
to Teensy2/Teensy2++.

https://www.pjrc.com/teensy/prescaler.html
 All use F_CPU = 16000000

Signed-off-by: Osamu Aoki <osamu@debian.org>