drm/xe/topology: Use register array size instead magic number

drm/xe/topology: Use register array size instead magic number

Since we keep registers in the array we can simply count them and
stop relying on magic number when checking if didn't make mistake.

Also we can switch to use xe_gt_assert() since it could be just
our programming mistake during platform bringup, no need to keep
drm_WARN() in the production driver.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://lore.kernel.org/r/20250604202908.769-3-michal.wajdeczko@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>