UefiPayloadPkg:Remove x86 legacy UART defaults

The BaseSerialPortLib16550 does fallback to a fixed address UART defined
by PcdSerialRegisterBase and does not initialize if it is zero. Do not
assume a serial port at 0x3F8, otherwise it could cause errors during
initialization of a non-existent serial port on non legacy platforms.

Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Signed-off-by: Marcello Sylvester Bauer <marcello.bauer@9elements.com>
Reviewed-by: Maurice Ma <maurice.ma@intel.com>
Reviewed-by: Guo Dong <guo.dong@intel.com>