exiv2: add patch to fix build error with some toolchains

This patch remove a header inclusion that is not required an can create
build error with some toolchains.
The patch is pushed on the upstream for the next release.
http://dev.exiv2.org/issues/1007

Fixes:
http://autobuild.buildroot.net/results/09d/09d9b525eeee458247e10a7948070c00bbabb964/



Signed-off-by: Nicolas Serafini <nicolas.serafini@sensefly.com>
Tested-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>