ARM: socfpga: Convert to DM serial

ARM: socfpga: Convert to DM serial

Pull the serial port configuration from DT and use DM serial instead
of having the serial configuration in two places, DT and board config.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Chin Liang See <chin.liang.see@intel.com>
Cc: Dinh Nguyen <dinguyen@kernel.org>