drm/xe: Clarify number of dwords/qwords stored by MI_STORE_DATA_IMM

MI_STORE_DATA_IMM can store either dword values or qword values, and can
store more than one value if the instruction's length field is large
enough.  Create explicit defines to specify the number of dwords/qwords
to be stored, which will set the instruction length correctly and, if
necessary, turn on the 'store qword' bit.

While we're here, also replace an open-coded version of
MI_STORE_DATA_IMM with the common macros.

Bspec: 60246
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20231016163449.1300701-11-matthew.d.roper@intel.com


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