drm/xe: Replace RING_START_UDW by u64 RING_START

drm/xe: Replace RING_START_UDW by u64 RING_START

Other u64 registers are printed in a single line so RING_START
needs to follow that too.
As there is no upstream decoder tool parsing RING_START this will
not break any decoder application.

Cc: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240510150108.80679-1-jose.souza@intel.com