cros-build: move Dockerfile to setup directory

Move the Dockerfile to the setup directory and change the context
accordingly.  This is to restrict the Docker context to the files that
are really needed, and avoid copying things like the cache and chroot
directories when rebuilding the container.
Signed-off-by: Guillaume Tucker <guillaume.tucker@collabora.com>

cros-build/docker-compose.yaml

@@ -2,7 +2,7 @@ version: '3'
 services:
   cros-sdk:
     build:
-      context: .
+      context: setup
       args:
         cros_device: ${CROS_DEVICE}
         cros_sdk_branch: ${CROS_SDK_BRANCH}

cros-build/Dockerfile → cros-build/setup/Dockerfile

@@ -56,4 +56,4 @@ RUN git config --global user.name cros-sdk-firmware
 RUN git config --global user.email cros-sdk-firmware@collabora.com
 ARG cros_device
 ENV CROS_DEVICE=$cros_device
-ADD --chown=cros-build setup/create-chroot.sh create-chroot.sh
+ADD --chown=cros-build create-chroot.sh create-chroot.sh