util/docker: Update docker files for coreboot-sdk & jenkins builders

- Check out the specific toolchain version we want before building
the toolchain (This version uses 1.42).
- Add additional libraries and tools needed to build coreboot related
packages.
- Move everything required to build any of the coreboot or related
packages into the coreboot-sdk from coreboot-jenkins-node Dockerfile.
- Separate the text of the commands in the Dockerfiles.
- Use nproc to get the number of processors for building the toolchain
- Add some additional comments about why things are done the way that
they are to the README
- Update the version of coreboot-sdk that coreboot-jenkins-node uses to
1.42. (This matches the toolchain version)
- Move ccache setup from jenkins-node to coreboot-sdk.
- Update the maintainer.

Change-Id: I293285ef72e3e70259355d924d425fea98ee773d
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/16239
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

util/docker/coreboot-jenkins-node/README.md

@@ -1,3 +1,10 @@
-run with
+This builds the coreboot tree in /dev/cb-build so that's a directory that uses
+a tmpfs.  This helps to speed up the build and doesn't write the output to
+the SSD.
 
-    docker run --privileged --restart=always -d -p 49151:49151 -v $host/path/to/ccache:/home/coreboot/.ccache -v $host/path/to/data/cache:/data/cache coreboot/coreboot-jenkins-node
+The encapsulate tool that the coreboot build runs under for security requires
+that docker be run using the --privileged command to work correctly.
+
+Run with the command:
+
+    docker run --privileged --restart=always -d -p 49151:49151 -v $host_path_to_ccache:/home/coreboot/.ccache -v $host_path_to_data_cache:/data/cache coreboot/coreboot-jenkins-node