drm/xe: Assume MTL's forcewake register continues to future platforms

Starting with MTL, the GT forcewake ack register moved from 0x130044 to
0xDFC.  We expect this change to carry forward to future platforms as
well, so forcewake initialization should use an IP version check instead
of matching the MTL platform specifically.

The (re)definition of FORCEWAKE_ACK_GT_MTL in the forcewake file is also
unnecessary; we can take the definition that already exists in the
dedicated register header.

Bspec: 65031, 64629
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>