Create buildroot config for arm64 unittests

Create a configuration that generates the rootfs image as well as qemu
host utilities to use for running kvm-unit-tests.

* Use sysv instead of busybox for licensing issues
* Add buildroot options to make the build isolated and reproducible
* Add dependencies required to run the kvm-unit-tests
* Append inittab to run /dev/vdb, which is assumed to have kvm-unit-test
* Build qemu for the host, support for aarch64-softmmu

Signed-off-by: Fuad Tabba <tabba@google.com>
diff --git a/configs/qemu_aarch64_virt_kvmunittests_defconfig b/configs/qemu_aarch64_virt_kvmunittests_defconfig
new file mode 100644
index 0000000..f22c01d
--- /dev/null
+++ b/configs/qemu_aarch64_virt_kvmunittests_defconfig
@@ -0,0 +1,38 @@
+BR2_aarch64=y
+BR2_OPTIMIZE_FAST=y
+BR2_FORCE_HOST_BUILD=y
+BR2_REPRODUCIBLE=y
+BR2_PER_PACKAGE_DIRECTORIES=y
+BR2_TOOLCHAIN_BUILDROOT_GLIBC=y
+BR2_PACKAGE_GLIBC_UTILS=y
+BR2_TARGET_GENERIC_HOSTNAME="kvmunittests"
+BR2_INIT_SYSV=y
+BR2_SYSTEM_BIN_SH_BASH=y
+BR2_TARGET_INITTAB_APPEND="test::wait:/bin/bash -c \"stdout_log=no bash /dev/vdb; poweroff\""
+# BR2_TARGET_GENERIC_GETTY is not set
+# BR2_TARGET_GENERIC_REMOUNT_ROOTFS_RW is not set
+# BR2_PACKAGE_BUSYBOX is not set
+BR2_PACKAGE_GZIP=y
+BR2_PACKAGE_GREP=y
+BR2_PACKAGE_SED=y
+BR2_PACKAGE_PYTHON3=y
+# BR2_PACKAGE_PYTHON3_UNICODEDATA is not set
+BR2_PACKAGE_OPENSSL=y
+BR2_PACKAGE_QEMU=y
+BR2_PACKAGE_QEMU_CUSTOM_TARGETS="aarch64-softmmu"
+BR2_PACKAGE_QEMU_FDT=y
+# BR2_PACKAGE_IFUPDOWN_SCRIPTS is not set
+BR2_PACKAGE_COREUTILS=y
+BR2_PACKAGE_COREUTILS_INDIVIDUAL_BINARIES=y
+BR2_PACKAGE_DEBIANUTILS=y
+BR2_PACKAGE_TAR=y
+BR2_PACKAGE_UTIL_LINUX=y
+BR2_PACKAGE_UTIL_LINUX_BINARIES=y
+BR2_PACKAGE_UTIL_LINUX_MOUNT=y
+BR2_TARGET_ROOTFS_EXT2=y
+BR2_TARGET_ROOTFS_EXT2_4=y
+BR2_TARGET_ROOTFS_EXT2_LABEL="rootfs"
+BR2_TARGET_ROOTFS_EXT2_SIZE="120M"
+# BR2_TARGET_ROOTFS_TAR is not set
+BR2_PACKAGE_HOST_QEMU=y
+BR2_PACKAGE_HOST_QEMU_SYSTEM_MODE=y