device: move .shared-patches to device/.shared-patches

All the downstream kernels reference ../../.shared-patches in their symlinks. Now that we have moved device ports to device/testing/*, those symlinks are no longer working.

Changing the path would require fixing all downstream packages and a new pmbootstrap release. Overall it seems easier to move the .shared-patches folder to device/.shared-patches.

Since it is only relevant for downstream kernel packages in device/ that might be a better place in general.