drm/xe/mmio: Drop compatibility macros

Now that all parts of the driver have switched over to using xe_mmio for
direct register access, we can drop the compatibility macros that allow
continued xe_gt usage.

v2:
 - Move removal of 8/16-bit read and xe_mmio_wait32_not() wrappers to
   this patch rather than removing them in earlier patches when last
   caller was removed.  (Rodrigo)

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240910234719.3335472-88-matthew.d.roper@intel.com