qemu: Updated version

* There are no longer any patches on QEMU for MicroBlaze or Zynq,
  mainline QEMU in 2.1.0+ provides functional models of MicroBlaze and
  Zynq machines
* Switch recipe to wildcard version as no version dependence exists in
  the bbappend

Signed-off-by: Nathan Rossi <nathan.rossi@xilinx.com>