[Natty, Oneiric] [SRU] Built-in some Xen drivers

[Stefan Bader]

https://bugs.launchpad.net/ubuntu/oneiric/+source/linux/+bug/886521

SRU justification:

Impact: Xen HVM guests (since around 2.6.36) will by default disable
(unplug) the emulated devices in favour of the paravirtualized drivers
when support for both is present (module or built-in).
This would make Xen installs more complicated (even if we put them into
a udeb because they are not getting autoprobed).

Fix: Change the configurations to have those (and the platform driver
which is recommended and actually non-configurable in 3.2 and later)
built-in.

Testcase: Installing a normal cdimage in HVM mode.

-Stefan