ARC: HAPS: use same UART configuration everywhere

For some reason we use ns8250 UART compatible on UP HAPS
configuration and ns16550a (which is ns8250 with FIFO support)
on SMP HAPS configuration.
Given that we have same UART IP with same IP configuration
on both HAPS configuration use ns16550a compatible everywhere.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>