package/qemu: bump to version 5.1.0

package/qemu: bump to version 5.1.0

Release 5.1.0 brought new changes like :
- New architecture support for AVR CPUs
- New ARMv8.2 TTS2UXN architecture feature support
- Parameter 'mem' of the '-numa' option is not supported anymore.

See:
https://wiki.qemu.org/ChangeLog/5.1
https://www.qemu.org/2020/08/11/qemu-5-1-0/

Build results available at : https://gitlab.com/jugurthaB/buildroot/-/pipelines/177823315.

Signed-off-by: Jugurtha BELKALEM <jugurtha.belkalem@smile.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>