[PATCH] Update QEMU to 5.2.0-rc1

[chrisj at rtems.org]

Hello,

This patch removed the previous git build of qemu and qem4 replacing it
with 5.2.0-rc1. I can build on FreeBSD and run the network tests for the
Xilinx Zynq BSP.

QEMU 5.2.0 has moved to the meson build system so you will need to make
sure you have Ninja install as meson layers on top of Ninja.

Please test on your preferred host and report any issues.

Thanks
Chris