arm: revert RHEL only preference for ACPI tables

We have been carrying a RHEL-only patch to prefer ACPI tables over devicetree when firmware presents both to the kernel. Upstream has preferred DT over ACPI. Very few systems ever presented both choices to the kernel and the only ones still doing so are old EOL systems. The approach that has been taken for a while now is for the DT/ACPI choice to be presented as a firmware option so that the kernel does not need to make the choice. For these reasons, it is time to get rid of the no longer needed RHEL-only option.