cpu-o3: Initialize register maps and free lists with loops.
cpu-o3: Initialize register maps and free lists with loops.

Now that these can be referenced by index instead of by a fixed name, we
can manage them more generically using loops.

Change-Id: I7bb7a6b712ee66f22fa809feef4abfcd1851f237
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49717
Reviewed-by: Giacomo Travaglini <8eef13a4f970e2e9372c8d26ad0737b760f99c02@arm.com>
Maintainer: Giacomo Travaglini <8eef13a4f970e2e9372c8d26ad0737b760f99c02@arm.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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