Add CI pipeline

.gitlab-ci.yml

+build:
+  tags:
+    - librem5
+  script:
+    - echo "man-db man-db/auto-update boolean false" | debconf-set-selections
+    - export DEBIAN_FRONTEND=noninteractive
+    - apt-get -y update
+    - apt-get -y install eatmydata
+    - eatmydata apt-get -y install build-essential gcc-aarch64-linux-gnu gcc-arm-none-eabi u-boot-tools mtools wget bison flex swig cpio bc kmod libssl-dev rsync git
+    - make librem5
+  artifacts:
+    paths:
+      - kernel-librem5.gz
+      - initramfs-purism-librem5.gz
+      - u-boot-librem5.bin
+      - src/purism-librem5.txt
+      - dtbs