package/qemu: Fix a regression in semihosting

The Buildroot's gitlab testing infra reported a build issue
with the qemu_arm_vexpress_tz_defconfig due to host-python3
modules issues [1]. Thoses issues has been fixed by the
previous patch.

But the defconfig doesn't boot with the current master
(2020.02-rc3).

It turn out that is an Qemu 4.2.0 regression that was
fixed upstream by [2]. This issue was found by using
git bisect old/new.

Fixes:
$ ../host/bin/qemu-system-arm -machine virt -machine secure=on -cpu cortex-a15 -smp 1 -s -m 1024 -d unimp -serial stdio -netdev user,id=vmnic -device virtio-net-device,netdev=vmnic -semihosting-config enable,target=native -bios bl1.bin
NOTICE:  Booting Trusted Firmware
NOTICE:  BL1: v2.0(release):2020.02-rc3-43-g9abf171ea6
NOTICE:  BL1: Built : 12:44:52, Mar  8 2020
ERROR:   Failed to load BL2 firmware.

After fixing host-python3 issue from [1]

[1] https://gitlab.com/buildroot.org/buildroot/-/jobs/456818689
[2] https://github.com/qemu/qemu/commit/21bf9b06cb6d07c6cc437dfd47b47b28c2bb79db



Signed-off-by: Adrien Grassein <adrien.grassein@smile.fr>
[Romain:
  - improve commit log
  - add upstream link
]
Signed-off-by: Romain Naour <romain.naour@smile.fr>
Cc: Etienne Carriere <etienne.carriere@linaro.org>
Cc: Gerome Burlats <gerome.burlats@smile.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>