scripts/make-release: ship u-boot source as a tarball

scripts/make-release: ship u-boot source as a tarball

The u-boot sources we ship currently cause problems with unpacking on
a case-insensitive filesystem due to path conflicts. This has been
fixed in upstream u-boot via commit 610eec7f, but since it is not
yet included in an official release we implement this approach as a
temporary workaround.

Once we move to a u-boot containing commit 610eec7f we should revert
this patch.

Cc: qemu-stable@nongnu.org
Cc: Alexander Graf <agraf@suse.de>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Thomas Huth <thuth@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-id: 20171107205201.10207-1-mdroth@linux.vnet.ibm.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
(cherry picked from commit d0dead3b6df7f6cd970ed02e8369ab8730aac9d3)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>