This commit adds a Bluetooth HCI UART lower half driver for the STM32

Squashed commit of the following:

    arch/arm/src/stm32:  Add Kconfig options needed by the HCI UART.  Various fixes to finally get a clean error free compile with no unexpected warnings.
    arch/arm/src/stm32:  In HCI UART, use spin_lock_irqsave() instead of enter_critical_section() whenever possible.
    arch/arm/src/stm32:  In HCI UART, fix up naming of configurations so that they are unique.  Still needs Kconfig settings.  Modify logic so that there can be multiple HCI UARTs, some supporting DMA and some not.
    arch/arm/src/stm32:  Integrate watermarks and software Rx flow control into the HCI UART driver.
    arch/arm/src/stm32:  Eliminate some HCI UART UART configuration options.  Per the HCI UART spec, the link will b 8 data bits, no parity, 1 stop bit... Always.
    arch/arm/src/stm32:  Trivial cleanup
    arch/arm/src/stm32:  Fixes most initial compilation issues STM32 HCI UART driver.  Still need to set up USART configuration parmeters for HCI UART
    arch/arm/src/stm32:  Completes first cut at STM32 HCI UART driver.
    arch/arm/src/stm32:  Completes most of read logic for HCI UART.  Still needs to be able to block if no read data is available.  Still missing write and flush logic.
    drivers/wireless:    Remove txenable from HCI UART methods.  arch/arm/src/stm32:  Reorganize some structures in HCI UART.
    arch/arm/src/stm32:  Still messaging the HCI uart driver.
    arch/arm/src/stm32:  Some trivial renaming.
    arch/arm/src/stm32:  A little more HCI-UART logic.
    arch/arm/src/stm32:  Initial setup to support HCI-UART.  Little more than the serial driver with some name changes and a few things removed.