drm/xe/tests/pci: Ensure all platforms have a valid GT/tile count

drm/xe/tests/pci: Ensure all platforms have a valid GT/tile count

Add a simple kunit test to ensure each platform's GT per tile count is
non-zero and does not exceed the global XE_MAX_GT_PER_TILE definition.

We need to move 'struct xe_subplatform_desc' from the .c file to the
types header to ensure it is accessible from the kunit test.

v2:
 - Rebase on latest xe_pci test rework from Michal and convert to
   a parameterized test that runs on each PCI ID supported by the
   driver.

Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Ravi Kumar Vodapalli <ravi.kumar.vodapalli@intel.com>
Link: https://lore.kernel.org/r/20250701201320.2514369-13-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>