support/docker: bump docker image for the gitlab-ci to Debian bullseye

support/docker: bump docker image for the gitlab-ci to Debian bullseye

Starting with Qemu 6.1.0, gcc 7.5 is needed to build.
Since we build host-qemu package for qemu defconfig, we have to
upgrade to (at least) Debian buster that provide gcc 8 as host compiler.

While testing this upgrate, the test_edk2 failed since it actually
requires Qemu >= 4.1.0 to support arm SBSA reference machine [1].
Debian Buster only provide Qemu 3.1.

Finally, upgrade to Debian bullseye but it requires some linux
kernel version bump in several defconfigs since host gcc is based
on gcc-10 [2].

[1] https://git.qemu.org/?p=qemu.git;a=commit;h=64580903c2b3aee08d74d64e6248a313b246cb69
[2] http://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/?id=621f2ded601546119fabccd1651b1ae29d26cd38

Signed-off-by: Romain Naour <romain.naour@gmail.com>
[Arnout: don't install python]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>