drm/i915/selftest: Add remap/rotate vma subtests when dst_stride!=width/height

Add selftests to test the POT stride padding functionality added in the
previous patch.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210325214808.2071517-25-imre.deak@intel.com