drm/i915/guc: Convert guc_mmio_reg_state_init to iosys_map

Now that the regset list is prepared, convert guc_mmio_reg_state_init()
to use iosys_map to copy the array to the final location and
initialize additional fields in ads.reg_state_list.

v2: Just use an offset instead of temporary iosys_map.

Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: John Harrison <John.C.Harrison@Intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220216174147.3073235-15-lucas.demarchi@intel.com