drm/xe: Rename instruction field to avoid confusion

There was both BLT_DEPTH_32 and XY_FAST_COLOR_BLT_DEPTH_32 - also add
the prefix to the first to make it clear this is about the FAST_**COPY**
operation. While at it, remove the GEN9_ prefix.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>