drm/xe: Separate number of registers from MI_LRI opcode

Keeping the number of registers to be loaded as a separate macro from
the instruction opcode will simplify some upcoming LRC parsing code.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20231016163449.1300701-10-matthew.d.roper@intel.com


Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>