write ioctl dispatcher
indicate arg type for each ioctl

fix a typo

Approved-by: Gregory Nutt <gnutt@nuttx.org>

XMC4xxx: Simply some USIC logic, add USIC interface to disable a channel.  Add USIC enable logic to UART configuration (a lot more to do there).

STM32F3: Add COMP support

Approved-by: Gregory Nutt <gnutt@nuttx.org>

XMC4xxx: Revise configuration for USICs.  Three USICs but 4 UARTs possible with each channel of USIC.