add UART6 and VBUS to BETAFPV F405
add alt config to BETAFPV-F405 to support RELAY2 instead of UART6_TX as per betaflight
enable SBUS input on BETAFPV-F405 on UART5_RX
enable IMU temperature calibration for BETAFPV-F405
correct current scale on BETAFPV-F405.
BETAFPV-F405 SPL06 Baro
correct baro SPI read rate on BETAFPV-F405
use SPL06 with background updates on BETAFPV-F405
setting up a DEFAULTGPIO pulldown in bootloaders is a bad idea as it
overrides any hardware pullups that have been put in place as part of
a "hold in bootloader" mechanism. See discussion in #27360 for ELRS
note that this only impacts one board that I can see, the
BlitzF745AIO, due to the MCU vs DEFAULTGPIO interaction
