sim: Provide an implementation for the pread64 system call.
sim: Provide an implementation for the pread64 system call.

This implementation is very similar to the pwrite64 system call, just
with data going the other direction as you'd expect.

Change-Id: I4f8ec9d83bf2339f9c84e31f25309c58e6157304
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/26603
Reviewed-by: Matthew Poremba <f1eb50f3368ce197c52b19f7fdb5aa7a278f15fd@amd.com>
Maintainer: Bobby R. Bruce <b9dba908ffb6c6d8ffe449cc88b3709c13c485c2@ucdavis.edu>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5