VRBRAIN: some updates from PX4 Firmware
stm32_i2c: handle more error conditions on I2C bus
mtd driver: add missing SPI header
stm32_serial: fixed spelling of FLOWCONTROL config option in stm32 serial code
CONFIG_ARCH_IRQPRIO: some updates from PX4 NuttX
VRBRAIN: change I2C timeout from 10ms to 1ms
VRBRAIN: new pre-compiled archives for all VR Brain boards
Added tone_alarm for VR Brain 5 and VR Micro Brain 5
Disabled buzzer and defined tone_alarm for VR Brain 5 PRO