drm/i915/xe2hpd: Do not program MBUS_DBOX BW credits

drm/i915/xe2hpd: Do not program MBUS_DBOX BW credits

No display IP beyond Xe_LPD+ has "BW credits" bits in MBUS_DBOX_CTL
register. Restrict the programming only to Xe_LPD+.

BSpec: 49213
CC: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Balasubramani Vivekanandan <balasubramani.vivekanandan@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240430172850.1881525-13-radhakrishna.sripada@intel.com