arm: amlogic: add setbrg op to serial device

Implement setbrg in amlogic/meson serial device with driver model
similar to how the meson_uart.c driver does it in Linux. Also
configure (probe) the serial device with the new reg5 register.

Signed-off-by: Edoardo Tomelleri <e.tomell@gmail.com>
Link: https://lore.kernel.org/r/20220918161701.572814-1-e.tomell@gmail.com


Acked-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>