drivers: serial: uart_mcux.c: add a feature macro wrap specific code

The enableRxRTS and enableTxCTS can only be configured when the
'UART_HAS_MODEM_SUPPORT' feature is enabled.
Uart has no 'error' IRQ on frdm_ke17z512, so update irq configuration
to configure the error interrupt when it exists.

Signed-off-by: Anke Xiao <anke.xiao@nxp.com>