Rename bootstrap_packages.x86_64 to bootstrap_packages.any

mkarchiso: look for bootstrap_packages.any or packages.any

If bootstrap_packages.${arch} or packages.${arch} do not exist, but bootstrap_packages.any or packages.any do, use them instead.

This allows to keep non-architecture-specific package list files without having to explicitly set the packages or bootstrap_packages variables in profiledef.sh.

Rename bootstrap_packages.x86_64 to bootstrap_packages.any

None of the packages listed in these files are architecture-specific. Allow reusing them on non-x86_64 architectures.