On gen11 the XY_FAST_COPY_BLT command has some size restrictions on its
usage.  Although this instruction is mainly used by userspace, i915 also
uses it to copy object contents during some selftests, so let's ensure
the restrictions are followed.

Bspec: 6544
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200311162300.1838847-3-matthew.d.roper@intel.comReviewed-by: José Roberto de Souza <jose.souza@intel.com>