petalogix-ml605: Set the MicroBlaze CPU version to 8.10.a

Set the MicroBlaze CPU version to 8.10.a avoiding a runtime
warning due to an unset CPU version.

Reviewed-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>