Fix bogus tests in the Atom category

- Atom Dual-core (Diamondville) is renamed to just Atom (Diamondville)
- The test with Atom D425 is named "Pineview", while the one with
  Atom D525 was incorrectly named "Cedarview". Moving the latter to
  atom-pineview-2.test and fixing its codename.
Add a test for Atom N2800 (codename Cedarview).
Fixed issue #7: Atom N2800

Reorganize the detection for Intel Atom CPUs

- no longer make the distinction between single- and dualcore CPUs.
- correctly handle all Pineview and Cedarview CPUs.