directfb: fix imlib image provider

Change 0002-imlib2-config.patch to patch configure.in instead of
configure to survicve the autoreconf step introduced by [1].

Fixes the following runtime error, e.g. from df_texture:

(!) Direct/Interface: Unable to dlopen `/usr/lib/directfb-1.6-0/interfaces/IDirectFBImageProvider/libidirectfbimageprovider_imlib2.so'!
    --> /usr/lib/directfb-1.6-0/interfaces/IDirectFBImageProvider/libidirectfbimageprovider_imlib2.so: undefined symbol: imlib_image_get_width

[1] http://git.buildroot.net/buildroot/commit/?id=7e9264956bb5693bc49274ee0b42ffb4c869e23f



Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>