drm/i915/dmc_wl: Rename lnl_wl_range to powered_off_ranges

drm/i915/dmc_wl: Rename lnl_wl_range to powered_off_ranges

In an upcoming change, we will add extra range tables for registers that
are touched by the DMC during DC states. The range table that we are
currently using is meant for registers that are powered off during DC
states. As such, let's rename the table to powered_off_ranges and also
add a comment regarding its purpose in the function that uses it.

Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241108130218.24125-9-gustavo.sousa@intel.com