drm/i915/adl_p: Require a minimum of 8 tiles stride for DPT FBs

The specification only requires DPT FB strides to be POT aligned, but
there seems to be also a minimum of 8 stride tile requirement. Scanning
out FBs with < 8 stride tiles will result in pipe faults (even though
the stride is POT aligned).

Signed-off-by: Imre Deak <imre.deak@intel.com>
Acked-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210506161930.309688-10-imre.deak@intel.com