drm/i915/dram: s/wm_lv0.../has_16gb_dimms/

The DRAM code shouldn't know anything about watermarks. Rename
wm_lv_0_adjust_needed to has_16gb_dimms. How this gets used is
up to the watermark code.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250902133113.18778-5-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>