drm/xe: Drop GT parameter to xe_display_irq_postinstall()

drm/xe: Drop GT parameter to xe_display_irq_postinstall()

Display interrupt handling has no relation to GT(s) on the platforms
supported by the Xe driver.  We only call xe_display_irq_postinstall
with the first tile's primary GT, so the single condition that uses the
GT pointer within the function always evaluates to true.  Drop the
unnecessary parameter and the condition.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20251013200944.2499947-27-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>