sim-se: factor out FutexMap::suspend and FutexMap::suspend_bitset

sim-se: factor out FutexMap::suspend and FutexMap::suspend_bitset

Both methods do basically the same, especially since they don't handle the
timeout which is basically the only difference between both modes of the
syscall (one uses absolute and the other relative time).

Remove the WaiterState::WaiterState(ThreadContext* _tc) constructor,
since the only calls were from FutexMap::suspend which does not use them
anymore. Instead, set the magic 0xffffffff constant as a parameter to
suspend_bitset.

Change-Id: I69d86bad31d63604657a3c71cf07e5623f0ea639
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/29776
Reviewed-by: Brandon Potter <Brandon.Potter@amd.com>
Maintainer: Brandon Potter <Brandon.Potter@amd.com>
Tested-by: kokoro <noreply+kokoro@google.com>