x86: Remove acpi=off boot parameter when ACPI is on

Remove the kernel boot parameter acpi=off so that kernel can turn on
ACPI support.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Tested-by: Stefan Roese <sr@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>