drm/xe: Move number of XeCore fuse registers to graphics descriptor

drm/xe: Move number of XeCore fuse registers to graphics descriptor

The number of registers used to express the XeCore mask has some
"special cases" that don't always get inherited by later IP versions so
it's cleaner and simpler to record the numbers in the IP descriptor
rather than adding extra conditions to the standalone get_num_dss_regs()
function.

Note that a minor change here is that we now always treat the number of
registers as 0 for the media GT.  Technically a copy of these fuse
registers does exist in the media GT as well (at the usual
0x380000+$offset location), but the value of those is always supposed to
read back as 0 because media GTs never have any XeCores or EUs.

v2:
 - Add a kunit assertion to catch descriptors that forget to initialize
   either count.  (Gustavo)

Cc: Gustavo Sousa <gustavo.sousa@intel.com>
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://patch.msgid.link/20260205214139.48515-3-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>