support/docker: add qemu-system-misc for riscv runtime tests

The docker image currently contains qemu-system-arm and
qemu-system-x86. Each package contains the 32bit and 64bit variants.
This has been sufficient for the time being.

The RISC-V ecosystem is growing rapidly. It is starting to become
mainstream. To increase the diversity in Buildroot runtime tests,
this commit adds the qemu-system-misc package in the Docker image,
in order to have the commands qemu-system-riscv{32,64}. This package
also contains other architectures (for example: microblaze, nios2,
s390x, xtensa, ...).

For Debian package details, see:
https://packages.debian.org/bullseye/qemu-system-misc

Signed-off-by: Julien Olivain <ju.o@free.fr>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

support/docker/Dockerfile

@@ -44,6 +44,7 @@ RUN apt-get -o APT::Retries=3 install -y --no-install-recommends \
         python3-pexpect \
         python3-pytest \
         qemu-system-arm \
+        qemu-system-misc \
         qemu-system-x86 \
         rsync \
         shellcheck \