drm/xe/guc: Cache DSS info when creating capture register list

Calculating the DSS id (index of a steered register) currently
requires reading state from the hwconfig table and that currently
requires dynamically allocating memory. The GuC based register capture
(for dev core dumps) includes this index as part of the register name
in the dump. However, it was calculating said index at the time of the
dump for every dump. That is wasteful. It also breaks anyone trying to
do the dump at a time when memory allocations are not allowed.

So rather than calculating on every print, just calculate at start of
day when creating the register list in the first place.

Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://lore.kernel.org/r/20250417213303.3021243-1-John.C.Harrison@Intel.com