drm/i915/dg2: Don't read DRAM info

DG2 does not use system DRAM information for BW_BUDDY programming or
watermark workarounds, so there's no need to read this out at startup.

Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210721223043.834562-18-matthew.d.roper@intel.com