intel/dev: Implement pixel pipe subslice counting for Gen12+.

intel/dev: Implement pixel pipe subslice counting for Gen12+.

Unlike Gen11, Gen12 hardware supports up to three pixel pipes per
slice.

Unfortunately the kernel interface is somewhat inconsistent between
Gen11 and Gen12: I915_PARAM_SUBSLICE_MASK returns a mask of enabled
*dual* subslices since TGL, so there is half the number of bits per
pixel pipe in the mask.  This is worked around here so we're able to
calculate the correct size of each pixel pipe, but the result is
returned in dual subslice units, inheriting the inconsistency from the
kernel -- Reason is that as of now all our Gen12 subslice counts
returned by gen_device_info.c are really dual subslice counts, and the
num_eu_per_subslice counts are also scaled accordingly, so it seems
like it would only make the matter worse if I fixed the units of this
field only without also fixing the rest.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8749>