Only ship flashrom on x86_64 for now (#122)

Dockerfile

@@ -88,7 +88,8 @@ RUN pip install uefi_firmware==v1.11
 
 # Install our custom flashrom package
 ADD https://github.com/metal-toolbox/flashrom/releases/download/v1.3.99/flashrom-1.3.99-0.el9.x86_64.rpm /tmp
-RUN rpm -ivh /tmp/flashrom*.rpm
+RUN if [[ $TARGETARCH = "amd64" ]] ; then \
+    rpm -ivh /tmp/flashrom*.rpm ; fi
 
 # Delete /tmp/* as we don't need those included in the image.
 RUN rm -rf /tmp/*