Changes introduced in commit d604a07225c5 ("build: add CycloneDX SBOM
JSON support") broke ImageBuilder:
Cannot open '/openwrt-imagebuilder-ath79-generic.Linux-x86_64/tmp/.packageinfo': No such file or directory
So lets fix it by wrapping the BOM generation behind condition of IB
feature check.
Fixes: #13881
Fixes: d604a07225c5 ("build: add CycloneDX SBOM JSON support")
Signed-off-by: Petr Štetiar <ynezz@true.cz>
(cherry picked from commit c4259a658673cc1a02ed17bfa8e94de17de00ad2)