Single arch and single flavour kernels ship an unordered config file

Single arch and single flavour kernels, such as the cloud kernels, are currently shipping a config file (that is installed under /boot) that is not properly ordered as the ones generated the master kernels.

The problem occurs because `make silendoldconfig` in "debian/rules.d/2-binary-arch.mk" does not re-writes the config file (and thus does not sort it) when no changes are made.

Although cloud kernels and other custom kernels are affected, the master kernels are the correct place to fix the problem. The custom kernels will inherit the fix automatically when rebased.