util: add pkg-config to ubuntu all-dependencies Dockerfiles

Without this, HDF5 is not built, e.g. a run such as
http://jenkins.gem5.org/job/Nightly/68/console contains:

Checking for hdf5-serial using pkg-config... pkg-config not found
Checking for hdf5 using pkg-config... pkg-config not found
Checking for H5Fcreate("", 0, 0, 0) in C library hdf5... (cached) no
Warning: Couldn't find any HDF5 C++ libraries. Disabling
         HDF5 support.

This is done to increase coverage a bit, and serve as dependency
documentation to users.

Change-Id: Ibf820a3aa76c29eeee1201646924ee181615a162
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/34777
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
diff --git a/util/dockerfiles/ubuntu-18.04_all-dependencies/Dockerfile b/util/dockerfiles/ubuntu-18.04_all-dependencies/Dockerfile
index 282805d..1259f2e 100644
--- a/util/dockerfiles/ubuntu-18.04_all-dependencies/Dockerfile
+++ b/util/dockerfiles/ubuntu-18.04_all-dependencies/Dockerfile
@@ -31,4 +31,4 @@
 RUN apt -y install build-essential git m4 scons zlib1g zlib1g-dev \
     libprotobuf-dev protobuf-compiler libprotoc-dev libgoogle-perftools-dev \
     python-dev python python-six doxygen libboost-all-dev libhdf5-serial-dev \
-    python-pydot libpng-dev libelf-dev
+    python-pydot libpng-dev libelf-dev pkg-config
diff --git a/util/dockerfiles/ubuntu-20.04_all-dependencies/Dockerfile b/util/dockerfiles/ubuntu-20.04_all-dependencies/Dockerfile
index 283d356..3facf7e 100644
--- a/util/dockerfiles/ubuntu-20.04_all-dependencies/Dockerfile
+++ b/util/dockerfiles/ubuntu-20.04_all-dependencies/Dockerfile
@@ -32,4 +32,4 @@
 RUN apt -y install build-essential git m4 scons zlib1g zlib1g-dev \
     libprotobuf-dev protobuf-compiler libprotoc-dev libgoogle-perftools-dev \
     python3-dev python3-six python-is-python3 doxygen libboost-all-dev \
-    libhdf5-serial-dev python3-pydot libpng-dev libelf-dev
+    libhdf5-serial-dev python3-pydot libpng-dev libelf-dev pkg-config