sim: Remove the byte_order parameter from System.

Instead, get the byte order from the workload. The workload has a better
idea what the byte order should be, for instance based on what software
it's loaded or how the hardware was configured, and this gets rid of a
use of TARGET_ISA which was setting a default endianness.

Change-Id: Ic5d8a6f69a664957c4f837e3799ff93397ccfc64
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/52106
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
2 files changed