scripts/ci: add build env rules for aarch32 on aarch64

scripts/ci: add build env rules for aarch32 on aarch64

At least the current crop of Aarch64 HW can support running 32 bit EL0
code. Before we can build and test we need a minimal set of packages
installed. We can't use "apt build-dep" because it currently gets
confused trying to keep two sets of build-deps installed at once.
Instead we install a minimal set of libraries that will allow us to
continue.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220225172021.3493923-8-alex.bennee@linaro.org>