drm/i915/bdw: s/BDW/BROADWELL for platform/subplatform defines

Follow consistent naming convention. Replace BDW with
BROADWELL.

Signed-off-by: Dnyaneshwar Bhadane <dnyaneshwar.bhadane@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230801135344.3797924-3-dnyaneshwar.bhadane@intel.com