drm/i915/selftests: tweak the misaligned_case

The compact-pt layout restrictions should only apply to the ppGTT. Also
make this play nice on platforms that only have the 64K GTT restriction,
and not the compact-pt thing.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Nirmoy Das <nirmoy.das@linux.intel.com>
Cc: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@linux.intel.com>
Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220420181613.70033-4-matthew.auld@intel.com