Support building images from outside of coreboot tree

scripts/_build/coreboot.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+
+set -e
+
+if [ -z "$1" -o ! -e "$1" -o -z "$2" ]
+then
+  echo "$0 [coreboot.config] [coreboot.rom]" >&2
+  exit 1
+fi
+CONFIG="$(realpath "$1")"
+COREBOOT="$(realpath "$2")"
+
+pushd coreboot >/dev/null
+  make CPUS="$(nproc)" crossgcc-i386
+  make distclean
+  cp -v "${CONFIG}" .config
+  make --jobs="$(nproc)"
+  cp -v "build/coreboot.rom" "${COREBOOT}"
+popd >/dev/null