utils/genrandconfig: add boot-wrapper-aarch64 handling

Fix the following build failure raised since the addition of the package
in commit 7689b72e:

configure: error: Could not find DTB file: /home/autobuild/autobuild/instance-9/output-1/build/linux-6.1.9/arch/arm64/boot/dts/.dtb

Fixes:
 - http://autobuild.buildroot.org/results/44287ccc8cc9767704642919e6d928d1f57b436d



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>