[DO NOT MERGE]Add Dockerfile to enable DockerHub auto build

Dockerfile

@@ -0,0 +1,41 @@
+#
+# Defines a docker image that can run Xtensa Qemu
+# This Dockerfile is used for DockerHub auto build
+#
+
+FROM ubuntu:18.04
+ARG UID=1000
+
+# Set up proxy from host
+RUN apt-get -y update && \
+	    apt-get install -y \
+		autoconf \
+		build-essential \
+		git \
+		python \
+		zlib1g-dev \
+		libglib2.0-dev \
+		libpixman-1-dev \
+		pkg-config \
+		sudo \
+		bsdmainutils
+
+# Set up sof user
+RUN useradd --create-home -d /home/sof -u $UID -G sudo sof && \
+echo "sof:test0000" | chpasswd && adduser sof sudo
+ENV HOME /home/sof
+
+# build qemu
+USER sof
+RUN cd /home/sof && git clone https://github.com/thesofproject/qemu.git && \
+	cd qemu && git checkout sof-stable && \
+# replace the submodule git repo to github mirror
+	sed -i 's#git://git.qemu.org#https://github.com/qemu#g' .gitmodules && \
+	sed -i 's#git://git.qemu-project.org#https://github.com/qemu#g' .gitmodules && \
+	./configure --prefix=`pwd`/ --target-list=xtensa-softmmu --enable-coroutine-pool && \
+	make
+
+# Create direcroties for the host machines sof directories to be mounted.
+RUN mkdir -p /home/sof/sof.git
+
+WORKDIR /home/sof/qemu/