[fix][lpc21] LPC + xbee_api in rotorcraft
workaround for lpc: sys_time_usleep only seems to work after a enableIRQ()
closes #350
update Parkzone T-28
[subsystems/electrical] fix conversion of vsupply to decivolts
* Should now work correctly with something like:
  <define name="VoltageOfAdc(adc)" value ="(VOLTAGE_ADC_SCALE * adc + VOLTAGE_OFFSET)"/> with VOLTAGE_OFFSET in Volts
* Also fix VoltageOfAdc to DefaultVoltageOfAdc in board header for tiny_2.0
[dfu] backport stm32 dfu flasher robustness fixes
- run sw/tools/dfu/stm32_mem.py --help for options
- by default now only upload to a device with idProduct containing "Lisa/M"
  - should prevent you from accidentally upload ap firmware to your BMP.
  - use '--product any' option to prevent checking of idProduct
[release] maintenance version 4.2.1