drm/i915: Rename the DSM/GSM registers

0x108100 and 0x1080c0 have been around since snb. Rename the
defines appropriately.

v2: Rebase

Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Acked-by: Nirmoy Das <nirmoy.das@intel.com>
Tested-by: Paz Zcharya <pazz@chromium.org>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240202224340.30647-7-ville.syrjala@linux.intel.com