airoha: an7581: enable uart baudrate control

airoha: an7581: enable uart baudrate control

The baud rate control on Airoha does not function properly. This
patch enables the inactive code responsible for this. The UART2
baud rate is correct. HSUART3 operates at twice the requested
baud rate. The same problem exists in the current code, so this
doesn't introduce any regression. Support for baud rates higher
than 460800 is still required. This will be added in the future.

Tested on Gemtek W1700k. UART2 and HSUART3 are working fine.

Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>
Link: https://github.com/openwrt/openwrt/pull/20049
Signed-off-by: Robert Marko <robimarko@gmail.com>