Prior to this change, setting of UART parameters like parity, stop bits or
data bits did not work correctly. As suggested by @iabdalkader, adding
__DSB() fixes the problem, making sure that changes to the UART LCR_H
register are seen by the peripheral.
Note: the FIFO is already enabled in the call to uart_init(), so the call
to uart_set_fifo_enabled() is not required, but kept for visibility.
Fixes issue #10976.
b7ea90d4cb