drm/xe: Drop gen afixes from registers

The defines for the registers were brought over from i915 while
bootstrapping the driver. As xe supports TGL and later only, it doesn't
make sense to keep the GEN* prefixes and suffixes in the registers: TGL
is graphics version 12, previously called "GEN12". So drop the prefix
everywhere.

v2:
  - Also drop _TGL suffix and reword commit message as suggested
    by Matt Roper. While at it, rename VSUNIT_CLKGATE_DIS_TGL to
    VSUNIT_CLKGATE2_DIS with the additional "2", so it doesn't clash
    with the define for the other register

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://lore.kernel.org/r/20230427223256.1432787-3-lucas.demarchi@intel.com


Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>