exiv2: XMP support needs largefile

XMP code enables largefile unconditionally.

Fixes:
http://autobuild.buildroot.net/results/116/1166068a64733d22a2f891849177ad826347dc9f/



Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Tested-by: Nicolas Serafini <nicolas.serafini@sensefly.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>