Remove unused code after refactoring all the serial/UART drivers.
() Since device initialization is done by the drivers themselves,
there is no need to have config_func(), port_init() and uart_init()
to perform configuration external to driver. So remove the related
bits.
() The IRQ priority is only being used when doing IRQ_CONNECT_STATIC().
So there is no need to send it over during uart_init().
Change-Id: I72eb3402036b53cbc01c1eb968de0ddfa0096ee2
Signed-off-by: Daniel Leung <daniel.leung@intel.com>