drm/xe: Track maximum GTs per tile on a per-platform basis

Today all of our platforms fall into one of three cases:
 * Single tile platforms with a single (primary) GT
 * Single tile platforms with two GTs (primary + media)
 * Two-tile platforms with a single GT (primary) in each

Our numbering of GTs has been a bit inconsistent between platforms
(e.g., GT1 is the media GT on some platforms, but the second tile's
primary GT on others).  In the future we'll likely have platforms that
are both multi-tile and multi-GT, which will make the situation more
confusing.  We could also wind up with more than just two types of GTs
at some point in the future.

Going forward we should standardize the way we assign uapi GT IDs to
internal GT structures.  Let's declare that for userspace GT ID n,

  GT[n]'s tile             = n / (max gt per tile)
  GT[n]'s slot within tile = n % (max gt per tile)

We don't want the GT numbering to change for any of our current
platforms since the current IDs are part of our ABI contract with
userspace so this means we should track the 'max gt per tile' value on a
per-platform basis rather than just using a single value across the
driver.  Encode this into device descriptors in xe_pci.c and use the
per-platform number for various checks in the code.  Constant
XE_MAX_GT_PER_TILE will remain just as the maximum across all platforms
for easy of sizing array allocations.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20250701201320.2514369-12-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>

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