drivers: serial: uart_mcux_lpuart: RX IRQ Enable RxOverrun flag

If the RX FIFO buffer is full and there's nothing being transmitted
no LPUART interrupt will fire anymore. Thus the application will not
receive any bytes anymore. By enabling kLPUART_RxOverrunInterruptEnable
we will receive interrupts even though RX FIFO is full so we can recover
from this.

Signed-off-by: Peter van der Perk <peter.vanderperk@nxp.com>