Begin building the Debian package on the SDK builders instead of a separate builder.

This adds the missing DEBs for the non-x64 architectures.

This avoids a repeated SDK build, which saves build time and guarentees the ZIP and DEB forms of the SDK have bitwise equal binaries.

Bug: https://github.com/dart-lang/sdk/issues/26953
Change-Id: I1bb33a77f5fc93c90b0fc7e7876fae5b7b69d7fc
Reviewed-on: https://dart-review.googlesource.com/c/recipes/+/430240
Commit-Queue: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Alexander Thomas <athom@google.com>