sim: Reintroduce the ignoreWarnOnceFunc syscall handler.

sim: Reintroduce the ignoreWarnOnceFunc syscall handler.

Instead of just using warn_once, we'll gate each warning on a bool
which is associated with the syscall desc pointer. To avoid having to
keep warn once bookkeeping in every syscall desc, we put it in a map
which is looked up at runtime.

Jira Issue: https://gem5.atlassian.net/browse/GEM5-187

Change-Id: I1dcce48de91b8a635f9f3df3bfc0ed6ba1291c4f
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23168
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Brandon Potter <Brandon.Potter@amd.com>