meta: add CI configuration

This commit adds a CI (and the Dockerfile it is based upon) that:
1. builds the HAL for the atsame70n21b and atsamv71q21b targets;
2. builds the board examples;
3. checks the formatting of all code except pac/; and
4. lints the code base with clippy, expect pac/.

Closes atsams-rs#21.

Author: tmplt

.ci/Dockerfile

@@ -0,0 +1,10 @@
+FROM rust:1.61.0-slim
+
+RUN apt-get update && apt-get install -y \
+  binutils-arm-none-eabi \
+  git \
+  && rm -rf /var/lib/apt/lists/*
+
+RUN rustup target add thumbv7em-none-eabihf && \
+    rustup component add rustfmt && \
+    rustup component add clippy

.ci/README.md

@@ -0,0 +1 @@
+This directory contains the `Dockerfile` used in the CI of the HAL. See [GitLab Container Registry documentation](https://git.grepit.se/embedded-rust/atsamx7x-hal/container_registry) for update instructions.

.gitlab-ci.yml

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+image: "registry.git.grepit.se/embedded-rust/atsamx7x-hal"
+
+stages:
+  - HAL
+  - examples
+  - lint
+
+default:
+  before_script:
+    - rustup show
+
+samv71q21b:
+  stage: HAL
+  script:
+    - cd hal
+    - cargo check --features samv71q21b,unproven
+
+same70n21b:
+  stage: HAL
+  script:
+    - cd hal
+    - cargo check --features same70n21b,unproven
+
+e70:
+  stage: examples
+  script:
+    - cd boards/atsame70_xpro
+    - cargo check --examples
+
+v71:
+  stage: examples
+  script:
+    - cd boards/atsamv71_xult
+    - cargo check --examples
+
+fmt:
+  stage: lint
+  needs: []
+  script:
+    - cd hal
+    - cargo fmt -- --check
+    - cd ../boards/atsame70_xpro
+    - cargo fmt -- --check
+    - cd ../atsamv71_xult
+    - cargo fmt -- --check
+
+clippy:
+  stage: lint
+  allow_failure: true
+  needs: ["samv71q21b"]
+  script:
+    - cd hal
+    - cargo clippy --no-deps --features samv71q21b,unproven
+    - cd ../boards/atsame70_xpro
+    - cargo clippy --examples --no-deps
+    - cd ../atsamv71_xult
+    - cargo clippy --examples --no-deps