uboot-tools: add patch to fix (no)stripping on non-ELF platforms

On Blackfin FLAT, stripping does not exist, but recent U-Boot versions
nonetheless try to strip and fail if they cannot do so. This commit
adds a U-Boot patch (submitted upstream) that solves this issue.

Fixes:

  http://autobuild.buildroot.org/results/153/1530f8247d1652da5779994f298141b1572ce74f/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>