drm/xe/mocs: Drop unwanted TGL table

TGL/RKL/ADLS/ADLP are all supposed to use the same MOCS table, with
values defined in the bspec.  Any entries listed in the bspec as
reserved/error/undefined should always be initialized to the most cached
and least coherent setting possible so that any userspace accidentally
referencing those undefined entries will only experience an increase in
coherency if spec updates down the road start defining real values.

The TGL and gen12 table entries defined in the driver today are
identical except that the TGL includes one additional (incorrect)
setting for table index 1.  Furthermore, the TGL-specific initialization
does not define a dedicated value for info->unused_entries_index, so
this incorrect table entry 1 also gets used to populate the MOCS
registers for all reserved/unused table entries.  This incorrect
behavior is a holdover from i915 where the platform was enabled with an
incorrect setting and by the time we noticed, it was too late to fix the
table without breaking ABI compatibility (and on TGL we did indeed have
some buggy userspace that was referencing the 'reserved' entry 1).
Since the Xe driver starts fresh with a clean slate on ABI, there's no
need to repeat the mistakes of i915 here.

v2:
 - Reword/clarify commit message.  (Lucas)

Bspec: 45101
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>