tests/docker: update and flatten debian-hexagon-cross

Update to the latest stable Debian. While we are at it flatten into a
single dockerfile as we do not some of the extraneous packages from
the base image to build the toolchain.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220914155950.804707-28-alex.bennee@linaro.org>

tests/docker/dockerfiles/debian-hexagon-cross.docker

@@ -2,12 +2,10 @@
 # Docker Hexagon cross-compiler target
 #
 # This docker target is used for building hexagon tests. As it also
-# needs to be able to build QEMU itself in CI we include it's
-# build-deps. It is also a "stand-alone" image so as not to be
-# triggered by re-builds on other base images given it takes a long
-# time to build.
+# needs to be able to build QEMU itself in CI we include its
+# build-deps.
 #
-FROM qemu/debian10
+FROM docker.io/library/debian:11-slim
 
 # Install common build utilities
 RUN apt update && \
@@ -15,11 +13,18 @@ RUN apt update && \
     DEBIAN_FRONTEND=noninteractive eatmydata \
     apt install -y --no-install-recommends \
         bison \
+        ca-certificates \
+        clang \
         cmake \
         flex \
+        gcc \
         lld \
+        make \
+        ninja-build \
+        python3 \
         rsync \
-        wget
+        wget \
+        xz-utils
 
 ENV TOOLCHAIN_INSTALL /usr/local
 ENV ROOTFS /usr/local
@@ -32,7 +37,7 @@ ADD build-toolchain.sh /root/hexagon-toolchain/build-toolchain.sh
 
 RUN cd /root/hexagon-toolchain && ./build-toolchain.sh
 
-FROM debian:buster-slim
+FROM docker.io/library/debian:11-slim
 # Duplicate deb line as deb-src
 RUN cat /etc/apt/sources.list | sed "s/^deb\ /deb-src /" >> /etc/apt/sources.list
 # Install QEMU build deps for use in CI