intel/dev: Split .num_subslices out of GEN12_FEATURES macro

intel/dev: Split .num_subslices out of GEN12_FEATURES macro

The .num_subslices field makes it problematic to reuse the
GEN12_FEATURES macro in other macros.

This also fixes the number of L3 banks for tgl gt1, except that this
was already fixed by Jason (dynamically) in:

86f67952d31 ("intel/devinfo: Compute the correct L3$ size for Gen12")

Cc: 20.1 <mesa-stable@lists.freedesktop.org>
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by : Lionel Landwerlin <lionel.g.landwerlin@intel.com>

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4955>