x86: acpi: Don't show the UART address by default

This is useful when using Linux's earlycon since the MMIO address must be
provided on some platforms, e.g.:

   earlycon=uart8250,mmio32,0xddffc000,115200n8

However this is only for debugging, so don't show it by default.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>