drm/xe/gt: Enable interrupt while initializing root gt

At present the interrupts are enabled while initializing the last GT. But this is incorrect for a Multi-GT platform, as root GT initialization will fail with interrupt disabled. Interrupts are required for the GuC submission triggered during initialization. Enable the interrupt during the root GT initialization.

Signed-off-by: Balasubramani Vivekanandan balasubramani.vivekanandan@intel.com